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Neutral Cable Heating

05/06/2014 7:25 AM

I am having a 1010 KVA Generator and using 6Core , 240 Sq mm , 3.5 Core Cable. When my load is going more than 700Amps the neutral cable is heating and its insulation is melting. Also on measuring current with clamp meter I am getting 250-300 Amp in neutral cables. What can be the reasons

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Power-User
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#1

Re: Neutral Cable Heating

05/06/2014 8:20 AM

Measure current in each phases, must be unbalanced. Also inform voltages in phases.

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Guru
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#2

Re: Neutral Cable Heating

05/06/2014 8:33 AM

"Penny-pinching", so use a neutral conductor that is properly sized instead.

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#3

Re: Neutral Cable Heating

05/06/2014 11:56 AM

Higher than expected unbalanced loads and smaller than required neutral conductors. Back to the drawing board....

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#12
In reply to #3

Re: Neutral Cable Heating

05/07/2014 7:42 AM

It's that simple. GA.

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Guru

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#4

Re: Neutral Cable Heating

05/06/2014 3:07 PM

Proper balance, proper conductor size= no problems.

PWSlack is probably right! Penny pinching never pays off.

If PWSlack is wrong, then fire your electrical "engineer"!

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Guru

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#6
In reply to #4

Re: Neutral Cable Heating

05/06/2014 6:00 PM

Oh dear. Two OT votes. I must have offended someone.

maddy1157, check the clutch, it may be slipping again.

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Guru
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#11
In reply to #6

Re: Neutral Cable Heating

05/07/2014 7:06 AM

<...must have offended someone...>

Baba Ji, probably...

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#15
In reply to #11

Re: Neutral Cable Heating

05/07/2014 10:06 AM

I CAN OFFEND ALMOST ANYONE. Usually without trying.

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Guru
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#5

Re: Neutral Cable Heating

05/06/2014 4:09 PM

<sigh> Back in 2011 you asked us how to calculate neutral conductor size for a generator.

You have two problems, your load and YOU!

Get someone qualified to do the work before you kill someone, the questions you are asking on CR4 clearly indicate you are NOT a qualified Electrician or Engineer and hence should NOT be doing this kind of work yourself.

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#17
In reply to #5

Re: Neutral Cable Heating

06/02/2014 7:15 AM

Guru my dear this set was running for some time approxx 300 Hours and now this problem started.

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Guru
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#18
In reply to #17

Re: Neutral Cable Heating

06/02/2014 3:40 PM

Unless the load has changed it sounds like the problem was always there and the neutral wire in the cable has been overheating and gradually failing for quite some time!

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Power-User

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#7

Re: Neutral Cable Heating

05/06/2014 11:06 PM

Check your all phase connections i believe you have connected the wrong phase on load somewhere in distribution. Balancing problem is very clear. Check by sequential shutting off the load one by one.

Looks like you are novice in the field. Recommend to the help and checked thoroughly before an accident happens.Dont take chances.

Neutral with 300 Amp is a blunder

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#8

Re: Neutral Cable Heating

05/07/2014 12:34 AM

Is it 6 runs of 3.5 x 240 sq.mm Aluminum cable. It is not clear from your posting the neutral current measurement.Each 240 sq mm cable can carry 400 A in open air without any derating and neutral 200 A.If the total neutral current is 250-300 Amps and if number of runs of cables is 6 then the each cable has to carry only 50 Amps , which is within rated current.

The heating of cable will occur when it is under sized or bad joints.

Please check whether all the 6 cables carry the neutral current equally.

Please also check for bad terminations.

The bad joint will generate heat.

Cable has to be derated for ambient temperature, method of laying,grouping,ground temperature etc.

if 6 runs of 240 sq.mm Aluminum cable, this will be just sufficient for 1010 kVA ,415 v ,50 hz generator .

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#9
In reply to #8

Re: Neutral Cable Heating

05/07/2014 3:27 AM

Shivaganti has it right...If the installation is optimum the neutral should carry no current. An unbalance in phase currents will show up as neutral current. Often electricians who don't know what they are doing will group single phase loads so that the three phase load is unbalanced causing a neutral current. A single large single phase load sometimes cannot be distributed to minimize the neutral current so you may be stuck there...Have fun...Clint

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#10

Re: Neutral Cable Heating

05/07/2014 4:41 AM

how is your protection? that is serious, a cable in any electric installation should not heat to that extent of melting insulation. what is the maximum current can that neutral line carry? 700Amps a big load. you need proper protection.

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#13

Re: Neutral Cable Heating

05/07/2014 8:28 AM

Loose connection or bad joint in neutral will cause local heating enough to melt insulation.

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Guru
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#14

Re: Neutral Cable Heating

05/07/2014 10:00 AM

If in doubt, consult a qualified Electrician.

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#16

Re: Neutral Cable Heating

05/07/2014 1:19 PM

If you mean 6-runs per phase of 240-sqmm 1-core cables, that means, 3runs of 240sqmm 1-core cables for neutral. This arrangement should easily handle 300A of neutral current that you found during measurement.

As some of the colleagues above already suggested, the problem could be cable termination, lug crimping or cable connection tightness.

Hope the above is helpful. Please share your findings.

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#19

Re: Neutral Cable Heating

09/27/2014 1:30 PM

i have same problem in my installations, we have 300 or more nos of cfl lamps in one floor, and currents in each phase cable almost same, then neutral current should be differnce between them, but we got neutral current 3 times of single phase current value. it causing neutral wire melting,

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Users who posted comments:

Clintb32 (1); DmanEng (1); Happy singh (1); horace40 (1); jack of all trades (2); lyn (3); maddy1157 (1); PWSlack (3); raghun (1); RAMConsult (1); ramvinod (1); Santhoshos103 (1); shivaganti (1); Wal (1)

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