Cable current carrying capacity

[Abe]

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]

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

[frank]

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]

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]

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]

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]

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?

[rbartlett]

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

[botrous]

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]

Hows this

Don't forget to apply good earth bonding

[botrous]

frank , did the tip of the msword thing worked ?

[frank]

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]

It's mostly effective for larger files

[Abe]

Frank

I printed it out and it came out great

Thx a million

Abe

[botrous]

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]

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]

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]

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

[chemi-cool]

But in that case, which is not bad, you need special heaters for 380 volt.

Chemi

[botrous]

Yes but look to the formula of capacity , you will get a lot more of wattssss

[Peter_1]

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.

[Abe]

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]

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

[Peter_1]

Why not just pulling a simple 5 wire cable (RST , N and earth).
You don't have to calculate this.
The AMPs through the neutral wire can never become larger than the AMp's through the live wires.

[botrous]

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]

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]

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.

[Peter_1]

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]

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]

Hi botrous,
Yes putting 2 heaters in series should half the voltage.

[botrous]

Hope things will go well Aiyub . . . . please provide us with the diagram you finally choose

Regards

[botrous]

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

[botrous]

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

[Peter_1]

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]

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]

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]

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

[Krups]

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]

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]

And its not 2.5 mm for all 6 heaters.....

Its one 2.5mm per phase

[chillin out]

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?)

[botrous]

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]

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]

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.

[Peter_1]

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]

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