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Thread: Cable current carrying capacity
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17-09-2005, 04:12 PM #1
Cable current carrying capacity
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
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17-09-2005, 04:59 PM #2
Re: Cable current carrying capacity
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
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17-09-2005, 06:06 PM #3
Re: Cable current carrying capacity
Originally Posted by Aiyub
This is also dependant on the installation -surface mount, conduit etc etc- and the enviroment it's situated in
cheers
richard
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17-09-2005, 06:24 PM #4
Re: Cable current carrying capacity
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.
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17-09-2005, 07:29 PM #5
Re: Cable current carrying capacity
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
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17-09-2005, 08:56 PM #6
Re: Cable current carrying capacity
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
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17-09-2005, 08:56 PM #7
Re: Cable current carrying capacity
The current may allways be 16 AMPS for a 1,5 mm˛ and 20 A for a 2 mm˛- 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?Last edited by Peter_1; 17-09-2005 at 10:12 PM.
It's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.
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17-09-2005, 09:18 PM #8
Re: Cable current carrying capacity
hi frank,
It is not true what you have written. How a 1.5mm can hold more than 2.5mm?????IF AT FIRST YOU DON`T SUCCEED.
DESTROY ALL EVIDENCE THAT YOU TRIED!
and go get a cuppa
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17-09-2005, 10:53 PM #9
Re: Cable current carrying capacity
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 vaporizerLast edited by Argus; 07-02-2011 at 08:30 AM.
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18-09-2005, 09:57 AM #10
Re: Cable current carrying capacity
Originally Posted by ArgusLast edited by Peter_1; 18-09-2005 at 11:33 AM.
It's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.
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18-09-2005, 10:59 AM #11
Re: Cable current carrying capacity
Originally Posted by Peter_1
Peter
Dont apologise, this is a general question and all input is desirable.
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18-09-2005, 12:22 PM #12
Re: Cable current carrying capacity
the current carrying capacity for a 2 core cable single phase is 19.5A for 1.5 cable and 27A for 2.5 cable.
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?Last edited by frank; 18-09-2005 at 12:26 PM.
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18-09-2005, 12:43 PM #13
Re: Cable current carrying capacity
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.
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
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18-09-2005, 03:11 PM #14
Re: Cable current carrying capacity
Originally Posted by Peter_1
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.
.
________
teen vidsLast edited by Argus; 07-02-2011 at 08:30 AM.
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18-09-2005, 05:40 PM #15
Re: Cable current carrying capacity
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?
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
ThxLast edited by Abe; 18-09-2005 at 05:48 PM.
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18-09-2005, 05:42 PM #16
Re: Cable current carrying capacity
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
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18-09-2005, 05:44 PM #17
Re: Cable current carrying capacity
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
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18-09-2005, 05:46 PM #18
Re: Cable current carrying capacity
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 Ł20.00 for each!!!
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18-09-2005, 05:50 PM #19
Re: Cable current carrying capacity
Each heater is about 3.5Metres long............yes
Its a blerry big evaporator
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18-09-2005, 06:05 PM #20
Re: Cable current carrying capacity
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.
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18-09-2005, 06:31 PM #21
Re: Cable current carrying capacity
Frank
Are u able to provide a "drawing" how this is done
Thx
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18-09-2005, 06:58 PM #22
Re: Cable current carrying capacity
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!
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18-09-2005, 07:03 PM #23
Re: Cable current carrying capacity
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
regardsEngineering, sciences, math, physics and my brain will generate "not responding " soon
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18-09-2005, 07:31 PM #24
Re: Cable current carrying capacity
Hows this
Don't forget to apply good earth bonding
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18-09-2005, 07:35 PM #25
Re: Cable current carrying capacity
frank , did the tip of the msword thing worked ?
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18-09-2005, 07:41 PM #26
Re: Cable current carrying capacity
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
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18-09-2005, 07:48 PM #27
Re: Cable current carrying capacity
It's mostly effective for larger files
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18-09-2005, 08:17 PM #28
Re: Cable current carrying capacity
Frank
I printed it out and it came out great
Thx a million
Abe
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18-09-2005, 11:04 PM #29
Re: Cable current carrying capacity
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.Last edited by Peter_1; 18-09-2005 at 11:08 PM.
It's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.
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19-09-2005, 05:47 AM #30
Re: Cable current carrying capacity
Not connecting the neutral in a 3 phase star connection wiring when more the 3 heaters is dangerous.
Abe
You should also install some high temp protection in your control circuit - what would happen if your contactor welded on?
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19-09-2005, 12:25 PM #31
Re: Cable current carrying capacity
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 . . . .Engineering, sciences, math, physics and my brain will generate "not responding " soon
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19-09-2005, 05:13 PM #32
Re: Cable current carrying capacity
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.It's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.
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19-09-2005, 06:38 PM #33
Re: Cable current carrying capacity
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
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19-09-2005, 08:28 PM #34
Re: Cable current carrying capacity
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
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19-09-2005, 08:42 PM #35
Re: Cable current carrying capacity
But in that case, which is not bad, you need special heaters for 380 volt.
Chemi
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19-09-2005, 09:05 PM #36
Re: Cable current carrying capacity
Yes but look to the formula of capacity , you will get a lot more of wattssss
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19-09-2005, 09:16 PM #37
Re: Cable current carrying capacity
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.It's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.
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19-09-2005, 09:24 PM #38
Re: Cable current carrying capacity
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
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19-09-2005, 09:27 PM #39
Re: Cable current carrying capacity
like we still have here in many places in Belgium
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 dropEngineering, sciences, math, physics and my brain will generate "not responding " soon
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19-09-2005, 11:53 PM #40
Re: Cable current carrying capacity
But in that case, which is not bad, you need special heaters for 380 volt.IF AT FIRST YOU DON`T SUCCEED.
DESTROY ALL EVIDENCE THAT YOU TRIED!
and go get a cuppa
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20-09-2005, 12:05 AM #41
Re: Cable current carrying capacity
Not if you wired 2 heaters in series between the phases.
Are you suggesting to reduce the voltage using the heater as a voltage divider ?
RegardsEngineering, sciences, math, physics and my brain will generate "not responding " soon
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20-09-2005, 12:22 AM #42
Re: Cable current carrying capacity
Hi botrous,
Yes putting 2 heaters in series should half the voltage.
IF AT FIRST YOU DON`T SUCCEED.
DESTROY ALL EVIDENCE THAT YOU TRIED!
and go get a cuppa
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20-09-2005, 09:17 AM #43
Re: Cable current carrying capacity
There is no problem connecting 7 or 8 heaters in an evaporator, as long as the neutral is connected in the starpoint.
I am on site 2 moro. Going to connect them your way
Can u provide a drawing what u mean starpoint for neutral
Thx
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20-09-2005, 10:03 AM #44
Re: Cable current carrying capacity
Originally Posted by Aiyub
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.
.
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teen videosLast edited by Argus; 07-02-2011 at 08:30 AM.
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20-09-2005, 11:19 AM #45
Re: Cable current carrying capacity
Hope things will go well Aiyub . . . . please provide us with the diagram you finally choose
RegardsEngineering, sciences, math, physics and my brain will generate "not responding " soon
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20-09-2005, 11:35 AM #46
Re: Cable current carrying capacity
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.It's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.
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20-09-2005, 11:40 AM #47
Re: Cable current carrying capacity
The AMPs through the neutral wire can never become larger than the AMp's through the live wires
regardsEngineering, sciences, math, physics and my brain will generate "not responding " soon
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20-09-2005, 12:12 PM #48
Re: Cable current carrying capacity
Originally Posted by chillin out
I don't like this option and connect therefore the neutral.It's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.
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20-09-2005, 12:35 PM #49
Re: Cable current carrying capacity
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 failEngineering, sciences, math, physics and my brain will generate "not responding " soon
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20-09-2005, 02:24 PM #50
Re: Cable current carrying capacity
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...
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