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Abe
17-09-2005, 04:12 PM
Flexible core cable
1.5 mm
2.5 mm

Over a 10 metre length what is the maximum amps the cable is capable of handling? for 1.5mm and 2.5 mm

Thx in advance

Abe

phil
17-09-2005, 04:59 PM
Flexible cables are usually rated for a 3kw max rating if you need to ask this question i suggest you get a qualified electrician to check it out for you

You can find cable ratings in the IEE onsite guide and the regulations
The units you are installing should state in the literature what supply you require
also if it is a new circuit on a domestic fuse board part P of the buliding regulations also needs to followed ie testing and certification

maddfridge

rbartlett
17-09-2005, 06:06 PM
Flexible core cable
1.5 mm
2.5 mm

Over a 10 metre length what is the maximum amps the cable is capable of handling? for 1.5mm and 2.5 mm

Thx in advance

Abe


This is also dependant on the installation -surface mount, conduit etc etc- and the enviroment it's situated in

cheers

richard

frank
17-09-2005, 06:24 PM
Hi Abe

The current capacity of a cable is dependant upon a number of factors, ambient temperature, installation method, type of fuse used etc and there are a number of different factors that have to be applied to the calculations.

If at the end of the calculation the voltage drop does not exceed 4% then the cable is safe to use. (9.2v for single phase and 16v for 3 phase.

The calculation is - volt drop = (mv/A/m) x Ib x L/1000

where
mv/A/m is the voltdrop (mv) per amp per metre taken from tables

Ib is the current drawn by the device

L is the length of the cable

To work out if your volt drop is less than 4% you must carry out the calculation. Using the figures from table 6E2 the (mv/A/m) volt drops are
1.5mm2 = 29
2.5mm2 = 18

From table 6E1of the On Site guide (Multicore Cables having PVC insulation) installation method 1 - clipped direct, the current carrying capacity for a 2 core cable single phase is 19.5A for 1.5 cable and 27A for 2.5 cable.

It isn't any good just saying that the regs say " 1.5mm can carry 19.5amps" so I'll use that - if you had a unit running at 16amps but 150m of 1.5mm2 cable then the result would be a volt drop of 69.6Amps or 29%. You can see now why you have to look at more than what you asked. :)

chemi-cool
17-09-2005, 07:29 PM
hi frank,
It is not true what you have written. How a 1.5mm can hold more than 2.5mm?????

we use flexibles up to 12amps for 1.5mm and 16amps for 2.5mm.

Thats the running currant. Using more will get it hot and eventually melt the PVC coating.
I would advice you to use a cable called XLPE, for the maximum run and at the end, make a connection box and continue with the flexible.

Chemi:)

Abe
17-09-2005, 08:56 PM
Ill pass more info at this point
Ive installed a 20 Kw evaporator
It has 8 heaters

We have connected 4 heaters

I checked the amp draw for the 4 heaters

Pulling 20 amps total for 4 heaters

I want to connect the other 4 as well

What Im going to do is this

Feed 3 seperate lengths of 2.5mm flex cable

Connect each cable to one phase from 3 phase supply

So ill connect 3 heaters to one phase
another 3 to second phase
and remainder 2 heaters to third phase

the run from the isolator, control paNEL to the evaporator is around 5 metres

But, the armoured 3 phase run from MAIN DISTRIBUTION board to the control panel is around 20 metres

Peter_1
17-09-2005, 08:56 PM
The current may allways be 16 AMPS for a 1,5 mm² and 20 A for a 2 mm²- at least in Belgium - whatever length the cable may be and that was the initial question of Aiyub.
But Frank has also a point that you will have a voltage drop,especially at high max AMPS. But the current remains the same value.
Is there in the UK also a regulation for selecting fuses according to the distance of the length of the cable from the switch-cupboard to the high voltage transformer?

chillin out
17-09-2005, 09:18 PM
hi frank,
It is not true what you have written. How a 1.5mm can hold more than 2.5mm?????
Where does he say that? did i miss something?

Argus
17-09-2005, 10:53 PM
The rules on the selection and rating of cables in the UK (I stress UK!) are precise and in BS 7671.

Appendix 4 deals with cable types, and rating factors, once the cable is determined the protective device is determined form Appendix 3.

What happens in other countries is irrelevant.

They are far too complex to summarise in a few sentences.
________
cheap easy vape vaporizer (http://vaporizer.org/reviews/easy-vape)

Peter_1
18-09-2005, 09:57 AM
What happens in other countries is irrelevant.

Sorry for asking, I was just curious.:rolleyes:

Abe
18-09-2005, 10:59 AM
Sorry for asking, I was just curious.


Peter

Dont apologise, this is a general question and all input is desirable.

frank
18-09-2005, 12:22 PM
the current carrying capacity for a 2 core cable single phase is 19.5A for 1.5 cable and 27A for 2.5 cable.

Hi Chemi

I think you have mistaken the volt drop per metre with what I wrote. ;)

Abe

If you are going to wire the heaters as described, I personally would not run 3 phase in flex cable unless it had some mechanical protection, such as SY or armoured. Why run 3 seperate cables? Can't you run singles in Copex?

How are you going to protect the circuits against overload/short circuit in the control panel?

Is the control panel protected by RCCD?

With a full load current for 3 heaters around 15A/phase + the fan load, the main armoured cable to the control panel should be a minimum of 2.5mm2. Are you running seperate neutrals to each set of heaters?

frank
18-09-2005, 12:43 PM
Hi Peter

British Standard 7671 (BS7671) is a set of electrical standards published by the Institute of Electrical Engineers in the UK. The standards are not a legal requirement but a set of standards which will ensure a safe and proper electrical installation. Some contracts specify that the electrical element of the installation will conform to BS7671 and so at this point they become legally binding on the installer.

http://www.iee.org/Publish/WireRegs/

The regulations cover all aspects, from fuse selection, wire sizing, earthing and bonding, special installations such as caravans, swimming pools, farming (cows are very suscepable to electrical shock from earthing grids) etc. and mostly all new or refurbishment work currently carried out in the UK complies with the regs. There is no defence in UK law if your electrical installation work kills someone - you will be charged with MURDER. :eek:

We also have a voluntary inspection council that anyone involved with electrical work can join http://www.niceic.org.uk/ and membership of this organisation gives credibility to your business as the customer knows you are working to set standards.

Argus is right about trying to explain the regs in a short sentence - it's just not possible :)

Argus
18-09-2005, 03:11 PM
Sorry for asking, I was just curious.:rolleyes:

Peter:

I wasn?t intending any nastiness; it's a fact that the safety rules for electrical installations throughout the EU have not been harmonised - probably never will be, as the task is far too big. The rule in the UK are distinctly different from any other countries.

Your other point about the distance from the network supply transformer in a previous reply is interesting.
The distance would certainly affect the supply impedance to the customer's terminals as would the quality of the network supply in terms of cable type, perturbation from other users etc. and would have a serious affect on the starting characteristics of motors.

There are indeed rules on this, not necessarily concerned with fuses or protective devices in the customer?s premises, though an excessive impedance will impact down the line. The rules are in fact EU law and contained in the EMC directive.

Abe:

Your idea of splitting the load across the 3 phases will give you an unbalanced load across the phases. One easier way out would be to fit an extra heater of equal loading and balance the lot.


.
________
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Abe
18-09-2005, 05:40 PM
If you are going to wire the heaters as described, I personally would not run 3 phase in flex cable unless it had some mechanical protection, such as SY or armoured. Why run 3 seperate cables? Can't you run singles in Copex?

I guess three singles in copex makes sense



How are you going to protect the circuits against overload/short circuit in the control panel?

Im providing circuit breakers for each phase



Is the control panel protected by RCCD?

I was not intending to use RCCD, but perhaps I should be


With a full load current for 3 heaters around 15A/phase + the fan load, the main armoured cable to the control panel should be a minimum of 2.5mm2. Are you running seperate neutrals to each set of heaters?

The main armoured is 2.5mm and has been provided by a proffessional electrician up to isolator point.

I need to know........Can I provide one single Neutral for all 8 heaters, or shall I provide a seperate neutral for each bank.......ie: 2 heaters per phase

Thx

Abe
18-09-2005, 05:42 PM
Abe:

Your idea of splitting the load across the 3 phases will give you an unbalanced load across the phases. One easier way out would be to fit an extra heater of equal loading and balance the lot.


I think instead of connecting all 8 heaters. I shall connect six..........2 per phase
I think each heater is drawing 5 amps, therefore total draw will be 10 amps per phase

frank
18-09-2005, 05:44 PM
I need to know........Can I provide one single Neutral for all 8 heaters, or shall I provide a seperate neutral for each bank.......ie: 2 heaters per phase

You can provide one single neutral wire for all heater elements but it must be sized to carry the whole load, i.e. 40A so it would need to be at least 10mm2

Abe
18-09-2005, 05:46 PM
This is the information I have on the heaters

Straight Rod
Rated 240 v
1500 W
Sheath Grade S231
Flush Moulded ends
3.5M tails


I bought 8 of them and fed them through the evaporator
Paid £20.00 for each!!!

Abe
18-09-2005, 05:50 PM
Each heater is about 3.5Metres long............yes
Its a blerry big evaporator

frank
18-09-2005, 06:05 PM
If you are going to balance the load out across the phases then you could star point the neutral and do away with the neutral wire. The supply must be through a triple pole mcb though. Basically, you would be turning the heater into a 3 phase heater.

Abe
18-09-2005, 06:31 PM
Frank

Are u able to provide a "drawing" how this is done

Thx

frank
18-09-2005, 06:58 PM
I'll have to e-mail it Abe due to the limit of the attachment size. Everytime I try to scan something in the file is huge!

botrous
18-09-2005, 07:03 PM
Frank , a little handy tip to handle and control the size of the attachements . . .

It's a little bit weird but effective , after scaning it , import it to microsoft word (insert picture) than save the file as webpage (in the saving dialog box , under the file name that you have to put choose save as webpage) , go to the directory you saved the file to , and you will find your file and a folder having the same name (samename_files) , open this folder , you find 2 pictures , the original and another one with a very minimal size . . .

Hope this helps
regards

frank
18-09-2005, 07:31 PM
Hows this

Don't forget to apply good earth bonding

botrous
18-09-2005, 07:35 PM
frank , did the tip of the msword thing worked ?

frank
18-09-2005, 07:41 PM
Hi Botrous

I pdf'd the document then saved the pdf as a jpeg - turned out to be 53kb so it uploaded. I created the drawing in Publisher which always ends up a large file so I Pdf'd first.

I will try your idea though.
Thanks

botrous
18-09-2005, 07:48 PM
It's mostly effective for larger files

Abe
18-09-2005, 08:17 PM
Frank

I printed it out and it came out great

Thx a million

Abe

Peter_1
18-09-2005, 11:04 PM
Not connecting the neutral in a 3 phase star connection wiring when more the 3 heaters is dangerous.

We had this discussion already once in the past and I then made a simulation with Multisim what will happen with the voltage and current through the remaining heaters when one of teh heaters fail.

This is the Law of Kirchoff.

Have a look once at http://www.tld-nv.com/peter/3-F.doc
It can take some seconds to download it.

To simulate a faulty heater, I inserted switches in serie wit the heaters so that I can switch off a heater.
On each line, I connected a digital current meter in line and a voltage meter parallel with the line.

You will notice 9 heaters and a 3 phase 3 *380 voltage source on the left side

Conclusion: connect always the neutral in the starpoint with heaters when there are more than 3 heaters. The heater in the drain line is also a heater so there are almost always more then 3 heaters.

frank
19-09-2005, 05:47 AM
Not connecting the neutral in a 3 phase star connection wiring when more the 3 heaters is dangerous.

Never found this to be a problem Peter. All 3 phase heaters that we purchase come as per my drawing. If you have good fusing then the imbalance through the MCB will trip the current supply in the case of a faulty heater circuit. Also, the RCCD should take care of any earth faults (heaters are notorius for shorting to ground)

Abe

You should also install some high temp protection in your control circuit - what would happen if your contactor welded on?

botrous
19-09-2005, 12:25 PM
Peter and frank , hi guys . . .
both of your point of vues seem acceptable to me . . . . . . the fuses have to play their role but relying on that isn't much a very good idea . . . .

Peter_1
19-09-2005, 05:13 PM
Frank,
Send this message to 5 manufactueres
2 answered already

If we have 6 or 8 heaters - at least more than 3 - in an evaporator, connected in star on a 400 V supply, do we have to connect the neutral wire in the starpoint?
Some of my colleagues say it isn't necessary at all, others - me included - say you certainly have to do it, otherwise you could have un unbalance whereby the remaining heaters will burn. (Law of Kirchoff)
What is your professional advice in this?

Helpman (The Netherlands)

Dear mr. Christiaen,

your point of view is correct.
the defrost will run, but, in unbalance or if one element is defekt, all others shall burn out.
Our advice is to connect the neutral to the star-point.
(by the way; burned elements don't be under warranty.
For further questions, don't hesitate to contact us.

Guntner Germany
In response to your question, yes I think you have to connect the neutral on these heaters, as the current must have a return path to stop them burning out. I think that your colleagues are applying the same theory as with motors, as not all motors will require a neutral, but just phase and earth, the reason being that the load can be balanced as some of the input can be lost in the windings etc. Heaters are different, if you dont connect the neutral they will burn out.


As soon I receive the others, I will post these.

chemi-cool
19-09-2005, 06:38 PM
Hi Peter.

I must have missed something.
Of course this is the only way to connect the heaters.

If there are are more then 3, there should be 6 of them.

I think manufacturers take it into consideration when they design the defrost heaters.

Chemi:)

botrous
19-09-2005, 08:28 PM
Guys why don't you just connect it in delta and have some peace of mind . . .
anyway i found this in a book that we have home since my father graduated (sure before my birth ) so take a look at it

Electric heaters basic installations :
3 phase

3 phases , star coupling , equilibrated circuit.Fig1:
The thermal receptor is formed of 3 equal resistors R coupled in star mode
U is the ddp between 2 phases of the main power supply and V the ddp between both sides of any resistor of the 3 (ddp between the live and the neutral) , I the current .
The capacity of the resistors will be :
P(watts)= 3VI=UI√3=(U^2)/R

NB: it's advised to connect the neutral line

3 phases , delta coupling , equilibrates circuit.Fig2:
I1 is the current in a resistor , all the other variables remains the same as above
The capacity of the resistors will be :
P(watts)=3UI1= UI√3=3(U^2)/R


Refference : Technologie des monteurs electriciens (Librairie DELAGRAVE) Chapter 4 pages 161 , 162

the pic was reproduced by me , so sorry for the bad resolution and layout

http://img5.picsplace.to/img5/5/image002_002.jpg

chemi-cool
19-09-2005, 08:42 PM
But in that case, which is not bad, you need special heaters for 380 volt.

Chemi:)

botrous
19-09-2005, 09:05 PM
Yes but look to the formula of capacity , you will get a lot more of wattssss :)

Peter_1
19-09-2005, 09:16 PM
Delta connection is only possible if the source is 3 x 220 V(like we still have here in many places in Belgium) or you need - like Chemi said - 30V heaters on a 3 x 380 V source.

They will heat more , that's for sure but they will burn very fast because you go beyond the specs of the manufacturer.

There is no problem connecting 7 or 8 heaters in an evaporator, as long as the neutral is connected in the starpoint.
Some manufactueres are placing straith rods in the battery and only a single wire is running to the other side of the coil - the neutral wire for the starpoint.

botrous
19-09-2005, 09:24 PM
Ah ok peter , here all the voltage is 220 V (between live and neutral ) and talking to my father , he said that they used to do it in delta for many years with no problems to heat the (fuel oil) in the power company tanks . . . and that they done sometime with the star coupling but they always connected a neutral to it

botrous
19-09-2005, 09:27 PM
like we still have here in many places in Belgium

Why , what's the voltage there 380 V for residential and commercial ???
Because here they don't allow more than 240 V for incidents reason , they were using 110V till 8 years ago when they switched all the country to 220 V and there were a lot of voices saying no to that , but the power company did it , i guess for reducing the power drop

chillin out
19-09-2005, 11:53 PM
But in that case, which is not bad, you need special heaters for 380 volt.
Not if you wired 2 heaters in series between the phases.

botrous
20-09-2005, 12:05 AM
Not if you wired 2 heaters in series between the phases.

Hi Chillin , how are you mate ?
Are you suggesting to reduce the voltage using the heater as a voltage divider ?

Regards

chillin out
20-09-2005, 12:22 AM
Hi botrous,
Yes putting 2 heaters in series should half the voltage.
:)

Abe
20-09-2005, 09:17 AM
There is no problem connecting 7 or 8 heaters in an evaporator, as long as the neutral is connected in the starpoint.


Peter

I am on site 2 moro. Going to connect them your way
Can u provide a drawing what u mean starpoint for neutral

Thx

Argus
20-09-2005, 10:03 AM
Peter

I am on site 2 moro. Going to connect them your way
Can u provide a drawing what u mean starpoint for neutral

Thx

This may have been mentioned before......

Before you do, please read BS 7671 (alias IEE 16th), Section 524, Reg 524-02-02.

It will help you to size the the neutral cable.

.
________
teen videos (http://teenvid.org)

botrous
20-09-2005, 11:19 AM
Hope things will go well Aiyub . . . . please provide us with the diagram you finally choose :)

Regards

Peter_1
20-09-2005, 11:35 AM
Why not just pulling a simple 5 wire cable (RST , N and earth).
You don't have to calculate this.:confused:
The AMPs through the neutral wire can never become larger than the AMp's through the live wires.

botrous
20-09-2005, 11:40 AM
The AMPs through the neutral wire can never become larger than the AMp's through the live wires

100% True . . . . . But the AMPs in the live wire can be more than the AMP's in the neutral in case of current leak . . . . that's why differential circuit breaker are made for . . . .

regards

Peter_1
20-09-2005, 12:12 PM
Not if you wired 2 heaters in series between the phases.

That's indeed an option but if one of the 2 fails, both will disfunction at once.
I don't like this option and connect therefore the neutral.

botrous
20-09-2005, 12:35 PM
The Job of good quality is always to stand on the safe side . . . I guess that's what you are doing Peter . . . .

No doupt that the best way to do this job is to wire a neutral , but that doesn't mean that other method don't work , and other methods can have protection devices againt incidents caused by a heater fail :)

Krups
20-09-2005, 02:24 PM
hi abe, when you get back could you give us a brief outline of how carried this job out please ?
and why you chose that particular course of action...

Abe
20-09-2005, 06:13 PM
Ill tell you why I chose Peters method........even before I go 2 moro to sort it

Peters looks to me the safest option........

I have all the circuit breakers and isolators.........

Cable will be 2.5 mm size

Ill take all the readings and post 2 moro

Abe
20-09-2005, 06:18 PM
And its not 2.5 mm for all 6 heaters.....

Its one 2.5mm per phase

chillin out
20-09-2005, 07:11 PM
Abe,

Be adventurous and go for the other option. You can then experiment and tell us how it goes.
:) :)
(you do have insurance don`t you?):p

Peter_1
20-09-2005, 07:44 PM
No doupt that the best way to do this job is to wire a neutral , but that doesn't mean that other method don't work , and other methods can have protection devices againt incidents caused by a heater fail :)

Sure, other methods can work fine.

We even installed safety motor current trippers instead of a fuse. So you can dial in very precise the current.
We then use the aux contact to trigger an alarm.

Same for protecting a transformer.

Regarding the current in the neutral due to an earth leak: in Belgium, the earth leak protetcor must cut-out when there is a leak of more than 300mA (in many cases even 30 mA)!, so this is not a big current.

When they're wired in serie - and suppose you wired the 2 drain pan heaters together - and one heater of the 2 fails, then all the water in the drain pan will become in ice, even so worse that it will push the drain pan away (seen it many times)
This isn't unsafe but you've inserted a possible fault that could give serious troubles.
We try to avoid possible errors.

In Belgium, it's not obligated to run the neutral over the contactor nor the main heater fuse. It may connected straigth to a 'neutral bar'
We never do this for the following reason: if you have an earth leak and all the neutrals are wired together, then it's almost impossible to find the eartleak. You have to losen all the screws on the bar beacause if you megger the circuit, the fault is everywhere and nowhere.

In an unbalanced system 3 phase system, there is always more current flowing through the live wires then the neutral but this doens't mean that there is an earth fault.
The example with the simulation shows this perfect.

We never calculate the AMPS for the neutral, just use a 5 wire cable.

Abe, it's indeed 2.5 mm² for every wire.

Another thing, we allways install a mechanical safety thermostat on the roof of a freezer and don't tell the client it's there. We dial in a fix setting and remove the knob of it.
We already had serious damage due to a failing electronic end-defrost systems.
We once had 7 ton of chicken meat in a poultry quick freezer which went to 95°C (!!) during the weekend.
Happily we were insured for this.
It was more a cooker then a freezer.
And once a freezer with +/-1.500 pastries in it in a bakery freezer.

frank
20-09-2005, 07:58 PM
Sure, other methods can work fine.

So what you are saying then Peter is that, with the correct safety measures in place, a 3 phase multi defrost heater installation can work just fine without a neutral connection?

Peter_1
20-09-2005, 09:13 PM
If you search once in the history of this forum, you will find exactly the same discussion.

The theory behind all this is the Law of Kirchoff and Marc O'Brien mentioned also the Thévenin Theorem which I forgot completely.

It all depends how many heaters are connected to the 3 phase system.
If more then 3 and some are connected in parallel without a neutral wire, then this is for the heaters - not the user - an unsafe situation.

Sure, connecting two in serie on 1 line is not unsafe as long as you don't connect heaters in parallel.
But connecting them in serie makes the installation more failure sensitive (if this is the correct English expression)

Other safety devices which can be used: overvoltage arresters, varistors, ... These devices works also fine but these are expensive solutions if you can use instead the (cheap) neutral wire.

We sometimes use varistors - which are very cheap - for the SV's in market trucks to protect them against overvoltage

Has nobody encountered in real life problems when the neutral is sudden lost along the electricity lines (outside your house)?

It was in the news some weeks ago but a worker here very nearby had in a transformer house disconnected the neutral accidendaly and +/- 160 houses had serious failures on electric components.

Still haven't got any other answers for the moment from manufacturers.

But why not try somebody this in theorey with some light bulbs and convince yourself? I have a strong feeling that this is something that most of us aren't aware of.
Take 8 bulbs of 220 VAC in 8 cheap sockets and connect them to a 3 phase 380-400 V power supply and see what happens.
Take voltage and AMP readings on the lines.
An example shows sometimes more than 1000 words.

Peter_1
23-09-2005, 07:11 PM
Dear Sir,
The elements connected in our coolers are always connected in star with a neutral line.

The reason is what you already say in your mail.


Some people connect the elements in our cooler without the neutral.
The number of elements is than always divided by 3.
If, in this case, one of the elements fails, the problem of unbalance arise.

Our "professsional" advice is, Use a neutral.

Best regards

Digni van der Zande
Office Sales Manager
Goedhart Cooling Equipment

frank
23-09-2005, 08:08 PM
If, in this case, one of the elements fails, the problem of unbalance arise.

As I've said before


with the correct safety measures in place

Peter_1
23-09-2005, 08:16 PM
Anyone tried the set-up with the light bulbs and unscrewing some to see what happens with the voltage?

chillin out
23-09-2005, 09:33 PM
Going by Franks wireing diagram, would you really get 240 v between phase and star-point?

If you think about the wave form of 3 phase, and then think about what you are doing with it.

When you measure between 2 phases you should get 415v , but then you introduce a third phase, this is out of sync with the other 2 by 120deg giving you 180v between any phase and star-point.

I think!!!!!

just throwing in some ideas.:) :) :)

botrous
23-09-2005, 09:45 PM
The star point is a neutral point , the voltage between the start point and any of the phases should be equal to voltage between 2 phases devided by the square root of 3...

Regards

Peter_1
23-09-2005, 09:56 PM
http://en.wikipedia.org/wiki/Three_phase

http://www.du.edu/~jcalvert/tech/threeph.htm

This is a good one:
http://www.electrician.com/electa1/electa4htm.htm

http://www.electrician.com/electa1/electa5htm.htm

http://www.electrician.com/electa1/electa3htm.htm

chillin out
23-09-2005, 10:31 PM
All of those links seem only to be concerned with currant and not voltage, which is what im talking about.

botrous.. I know the star-point is called 'neutral' but its not an actual no volts dead spot is it?

I will continue my googling.:) :)
Any points to prove/dissprove me are welcomed.

Abe
23-09-2005, 11:39 PM
All six heaters connected. 2 heaters per phase off a three phase supply
2 X 1500 watt heaters connected per phase
All of one 18 Amp Contactor


These are the readings.

12 amps draw per phase, so Im assuming each heater is drawing 6 amps

Each phase protected by a 16 amp type B circuit breaker and a 20 amp cartridge fuse at main Distribution box

Neutrals are ALL linked into one bus bar.

Ill go to site again next Wednesday to see if Evaporator is clear

I need to ask one other question

The drain line heater is permanently on and gets quite hot.
It is not self regulating.

Is that safe??

Peter_1
24-09-2005, 07:26 AM
All of those links seem only to be concerned with currant and not voltage, which is what im talking about.
botrous.. I know the star-point is called 'neutral' but its not an actual no volts dead spot is it?
I will continue my googling.:) :)
Any points to prove/dissprove me are welcomed.
Chillin, via the Law of Ohm, you can convert this to voltage ;)
The star point in NOT always A neutral point and certainly not THE neutral point. It's only neutral in a balanced field. In a balanced set-up it's indeed a 0-volt point and you don't have to connect it, ...like in an electrical motor where all 3 windings, so the load are equal.
Prove/dissaprove...go to the nearest electrical shop and buy for 5£ of material and a practical test shows more then 1000 words. But as I said previous, try to understand why this happens.
Google on Kirchoff and Thévenin.

botrous
24-09-2005, 11:40 AM
In a balanced set-up it's indeed a 0-volt point and you don't have to connect it, ...like in an electrical motor where all 3 windings, so the load are equal.


Peter , you made my point .
Chillin out , that's what I meant to say

frank
24-09-2005, 05:43 PM
When you measure between 2 phases you should get 415v , but then you introduce a third phase, this is out of sync with the other 2 by 120deg giving you 180v between any phase and star-point.
Hi Chillin
What you are seeing is the third phase acting as a neutral due to the phase shift. If you only have 2 phases requiring a neutral then a wire is needed. But with a balanced 3 phase load you do not need a neutral wire as one phase always acts as a neutral current path.

Have you ever noticed that you can measure voltage upto the load but only current from the load?

chillin out
24-09-2005, 10:10 PM
Thought about it and found that all I have to do is go to a comp which is wired in star (arctic circle as the star point is accessable) and measure it there, will do that tomorrow.(unless I get called out again tonight:mad: )

Have you ever noticed that you can measure voltage upto the load but only current from the load?
This true on a 2 phase motor?;)

Peter_1
25-09-2005, 07:17 AM
Between each fase and the copper star-bridge, you will measure 220 V.
Measure once between the bridge and earth (the copper lines connected to th compresser -->O V) and between a fase and the copper of the lines connected to the compresser (again 220 V)
Do you understand what's happening?

chillin out
25-09-2005, 05:29 PM
I think all is clear now, went to a site today and took measurements. 240v between phase and bridge.

Thanks all,:) :)

Peter_1
25-09-2005, 08:33 PM
What was the reading between line and ground and between bridge and ground?

If you haven't measured it, what should the reading be?

chillin out
25-09-2005, 09:47 PM
Didn`t measure it,


between line and ground
240v


between bridge and ground
0v

Peter_1
25-09-2005, 10:23 PM
You got it and I'm sure this is something you will now never forget anymore.
If you have some time, do once the test with the bulbs, you will learn even a lot more.