Melted neutral wires120/240

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Strombea

Strombea

Senior Member
Location
Prescott, Arizona, USA
Quick question,

I am an electrician in Arizona and I was called to repair and inspect a few melted 14 and 12 awg wires in the panel. None of the neutrals are shared and none seemed to be overloaded at the time (house could have had equipment plugged in overloading the neutral in the past). I cut them back and reinstalled to the buss, but out of curiosity I would like to know the reason a neutral (not shared) would melt or heat up before the hot wire does.(bad breaker or not, the current is the same through both wire, so why neutral hotter?)

No connections were loose or a cause for higher resistance.

I understand the electrons travel further on the neutral side as the hot side always has the electricity thus not traveling as far. Example: hot wire 100 ft to outlet with electrons already there, neutral wire 100 ft with no electrons until the circuit is closed. Is this the reason an unshared neutral will melt before the hot wire.

Not a big deal just thought I'd ask.
 
Were the nuetrals loose in the lugs?

Was this NM wire Hot nuetral ground.?

if all appears good I would turn off all circuits except for one of the melted circuits. Then I would load up that circuit and see if all the return current is on the corresponding nuetral. If not further test.
 
Is there any possibility that current flow on the neutral bar, unrelated to the circuits in question, caused enough heating to melt the insulation.

Is there any possibility that this is a 120V panelboard (not a 120/240 panelboard) and that _all_ of the system current is being carried by the neutral bar?

-Jon
 
Strombea said:
Quick question,

I am an electrician in Arizona and I was called to repair and inspect a few melted 14 and 12 awg wires in the panel. None of the neutrals are shared and none seemed to be overloaded at the time (house could have had equipment plugged in overloading the neutral in the past). I cut them back and reinstalled to the buss, but out of curiosity I would like to know the reason a neutral (not shared) would melt or heat up before the hot wire does.(bad breaker or not, the current is the same through both wire, so why neutral hotter?)

No connections were loose or a cause for higher resistance.

I understand the electrons travel further on the neutral side as the hot side always has the electricity thus not traveling as far. Example: hot wire 100 ft to outlet with electrons already there, neutral wire 100 ft with no electrons until the circuit is closed. Is this the reason an unshared neutral will melt before the hot wire.

Not a big deal just thought I'd ask.
Click to expand...

What type of construction? Residential? Commercial?
possible Harmonics issue?
 
Strombea said:
I was called to repair and inspect a few melted 14 and 12 awg wires in the panel. None of the neutrals are shared and none seemed to be overloaded at the time . I cut them back and reinstalled to the buss.

No connections were loose or a cause for higher resistance.
Click to expand...


If there was no loose connection then why was the neutral (conductor) only damaged in the area near the neutral buss?

I would guess that one or more of these connection was loose and caused a good deal of heat in this area.

Were the damaged neutrals all in the same area of the neutral buss?
 
What was melted, short length near the termination or long length - maybe even entire run?

Short length at the termination is a pretty good sign the termination had resistance in it and was heating up. The more current drawn the more heat is created in the connection. Usually only a short length of conductor (couple inches or so) is all that is overheated.

If the conductor is melted its entire length - much better sign of overloading. We don't put overcurrent devices in the grounded conductors so there is nothing to interrupt such overload.
 
One theory that has been put forward on another forum as to why these 'bad joint/connections not tight" issues always seem to involve the neutral connection involves human phycology.

The argument goes along the lines that we all realise that the HOT conductor is important and must be a good, solid connection so we make sure its good & tight.

The neutral, however, seems to be less 'important' and we (sub-consciously) don't take the same care to ensure that it is equally tight.

(I know that the current is the same in both the hot & neutral legs so both need to be equally good electrical connections).

Although we don't use MWB circuits here in the UK so we don't have the shared neutral issues that you guys have, we do still get problems with burnt wire/terminals from poor connections. These too seem to be almost exclusively on the neutral conductor terminations. One of the biggest culprits seems to be the instantaneous electric shower heater (often around 8- 10kW at 230V, so pulling 32 - 45A).

Adrian
 
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backstabing rectp

backstabing rectp

I had some recepticals that were backstabed and only the neutrals were burnt off, four in a row. Wonder if any connection.:blink:
 
just the cowboy said:
I had some recepticals that were backstabed and only the neutrals were burnt off, four in a row. Wonder if any connection.:blink:
Click to expand...

I see that so much too. I wonder if it's not the order most guys (myself and just about everybody I've seen) terminate neuts flip the device then hots, messing up the stab clips for the ones that were in when flipped? Idk Mabey the every once in awhile when you see hots burned it was a lefty:)
 
Thank you everybody

Thank you everybody

Thanks for the replies. I think that if you hypothetically heated up a circuit and overloaded it in a perfect environment the hot wire and neutral wire should melt or heat up equally. But more often than not the nuetral goes first.

Thanks again, i was curious.
 
Strombea said:
Thanks for the replies. I think that if you hypothetically heated up a circuit and overloaded it in a perfect environment the hot wire and neutral wire should melt or heat up equally. But more often than not the nuetral goes first.

Thanks again, i was curious.
Click to expand...

Consider this. The thermal dissipation of the breaker may be greater than that of the neutral bar. The breaker can act like a heat sink, sinking to the larger bus bars. The arrangement of the breakers may be different, too, distributing the heat more. Also, the spacing of the breakers is a tad wider.

The neutral bar has less mass and takes less energy to heat up. Heat causes oxidation, which causes heat, which causes oxidation......also, the conductors on the neutral bar may be arranged as to distribute the heat less.
 
K8MHZ said:
Consider this. The thermal dissipation of the breaker may be greater than that of the neutral bar. The breaker can act like a heat sink, sinking to the larger bus bars. The arrangement of the breakers may be different, too, distributing the heat more. Also, the spacing of the breakers is a tad wider.

The neutral bar has less mass and takes less energy to heat up. Heat causes oxidation, which causes heat, which causes oxidation......also, the conductors on the neutral bar may be arranged as to distribute the heat less.
Click to expand...
The breaker is also a thermal cut out, too much heat and it will trip.
 
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