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A
Anonymous
Unregistered
>I still think it sounds like an bad conection prob.
This is why I asked him whether the heat was at a hot spot. He said that it went on for 20' that he could feel.
In my opinion that is not consistent with a bad connection.

To me it sounds like heavily loaded wires. He appears to have at least 8 overloaded wires and two more at 99+% ampacity.

A
Anonymous
Unregistered
>pipe is aluminum,
Aluminum (versus plastic) is a decent enough conductor of heat that I would say that what you feel on the outside is representative of what is on the inside.

> 1 or 1-1/4", (fergot to check that)
It doesn't matter much. It sounds like you have 15 conductors in there.

>neutral 14.5 amps
It looks like your meter reads true RMS - which is good.


[This message has been edited by Dspark (edited 07-23-2001).]

Joined: Dec 2000
Posts: 4,294
Member
DSpark.
Would someone really run three circuits on one neutral with that type of lighting?
Yes, 4 wire circuits are used regularly to supply high bay lighting. It sounds like these hi-bays are 400w HPS or MH, as there are 9 per circ.
Circuit #2 is overloaded for a 20A circuit. What makes you think the neutrals are going to cook?? (Other than the 15-conductor derating issue).

A
Anonymous
Unregistered
>Circuit #2 is overloaded for a 20A circuit.
That's not the only one!

>What makes you think the neutrals are going to cook??
Harmonics. It's pretty obvious from the numbers that the neutrals are carrying more than just the imbalance.

Take circuits 1, 3, & 5 {15.1 A, 14.9 A, 15.5 A}. That's almost perfectly balanced.
But the neutral carries a whopping 6.0 amps which is about tens times the imbalance!

Take circuits 7 & 9, they are balanced. The neutral should be carrying 13.4 not 14.5.

When a neutral carries more than the imbalance, they can overload.

Do you doubt it?

Joined: Dec 2000
Posts: 4,294
Member
..a whopping 6 amps
On a #12?
..that's not the only one
What would you consider to be the allowable LCL on a 20 amp circuit? (it's 16A in the real world).
Are you trying to pull my leg?

Joined: Jul 2001
Posts: 599
J
JBD Offline
Member
Based on the number of conductors in the pipe, there is up to 10% overloading above the best case of 15A per #12 with 90 deg C insulation. We really don't have to look any further.

I would be remiss to recommend anything other than correction of this installation.

Most people forget how hot electrical devices are allowed to run. At full load most electrical devices are too hot to touch, but are still operating well below design levels. For example the operating handle area of a circuit breaker is allowed to be over 100 deg F, and is typically the hottest part of a panel

DS - Imbalances are currents which have not canceled, that they come from harmonics is immaterial. This is a 3 phase system circuits 7 & 9 would never cancel, the neutral current would be expected to about equal to the phases.

Joined: Dec 2000
Posts: 4,294
Member
I don't believe anyone is disputing the fact that this installation needs correction.
JBD - Being that these wires terminate in a breaker panel (with terminals rated @ 75°C), the 90° rating isn't applicable, is it?
DS - If your previously mentioned 22 wires had been installed, each of the neutrals would have been carrying the full load from their respective circuits. Wouldn't more heat be collectively generated by this?

A
Anonymous
Unregistered
>For example the operating handle area of a circuit breaker is allowed to be over 100 deg F, and is typically the hottest part of a panel
That is warm, not hot.

>Imbalances are currents which have not canceled
Correct.

>that they come from harmonics is immaterial.
Wrong. If they were vanilla 60 Hz sine waves, they would cancel.

>This is a 3 phase system circuits 7 & 9 would never cancel,[/b]
You misread. They are equal.

>the neutral current would be expected to about equal to the phases.
No, it should be exactly equal.
But it is a lot more.
That means that the normal cancelation of half per phase did not occur.

Look at the other circuits. They have the same problem.

A
Anonymous
Unregistered
>If your previously mentioned 22 wires had been installed, each of the neutrals would have been carrying the full load from their respective circuits. Wouldn't more heat be collectively generated by this?
Yes. That is why oversized neutrals are preferable.

But one neutral per circuit will not overload the neutral's ampacity. So there would be twice as much heat, but spread over three times as many conductors.

Joined: Dec 2000
Posts: 4,294
Member
Let me rephrase:
Wouldn't more heat be generated on each and every neutral conductor? Wouldn't each and every neutral be hotter carrying the c.15A loads rather than the "whopping 6 amps" that the 4 neuts carry?
(Remember, you're burning the insulation off).

[This message has been edited by electure (edited 07-24-2001).]

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