Hey guyz got a lighting problem for ya'll I have a lighting panel in which 11 of the 12 circuits leave the panel out of one pipe, and it's hot, all the brkrs are 20 amp, the wiring is #12, none are overloaded, I vaguely remember that nonlinear loads can mess up some types of loads, this panel has 9 ckts with hid metal halide, and 3 ckts with flurescents, (277v panel) could this be a harmonics problem????

You have 22 conductors in what size and type of pipe?

What is the ambient temperature?

Is the pipe pretty uniformly hot or is there a hot spot?

> none are overloaded,
Assuming that the circuit breakers are in working order, that probably has to be true based on the #12 takes 20 A generality.

But you have a problem. You've got over 9 conductors in one conduit and you did not derate. So just maybe they are way overloaded.

>I vaguely remember that nonlinear loads can mess up some types of loads,
On the branch side, that is a problem only when the neutrals are shared on a multiwire. In that case, the neutrals can be overloaded which means that you need to derate them even further.

Do you have 22 conductors for the eleven circuits or perhaps only 17?


To me it sounds like you need more conduits, heavier wire, and perhaps a neutral per circuit or oversized neutrals.


[This message has been edited by Dspark (edited 07-20-2001).]

Or perhaps 15 conductors?

[This message has been edited by electure (edited 07-20-2001).]

I check for heat a lot. The simple, quick assessment of placing a hand across the breakers in a panel says a lot.

customers can be given simple layman's terms.

Hot--Bad! Hot- Fire!

tajoch,

Can you give us more information? What type of wire is it, what are the loads on the circuits?

Assuming it is THHN and that you have a neutral per circuit your capacity would be down to 13.5 amps (45% of 30A) if you are anywhere near that load that explains where the heat is coming from. If you can change these wires to #10s or remove half of them you should be Ok.

Bill

Or perhaps 15 conductors?
I guess since this is apparently three phase! Would someone really run three circuits on one neutral with that type of lighting?

Perhaps his neutrals are about ready to melt their 90° thermoplastic off.

Putting half the wires in another conduit won't completely solve the heat problem if the neutrals need upsizing also.

Thanx guyz, it's a 277volt lighting panel, 20amp ckts, #12 thhn, pipe is aluminum, 1 or 1-1/4, (fergot to check that)
ckt 1 is 15.1A, (9 hid fixtures)
ckt 3 is 14.9A (9 hid's)
ckt 5 is 15.5A (9 hids)
neutral for 1,3,5 6.0 amps

ckt 2 16.7A (9hids)
ckt 4 6.6A 12 flurescents
ckt 6 15.2 (9 hids)
neutral 2,4,6, 15.5a

ckt 7 13.4A (8 hids)
ckt 9 13.4A (7 hids)
neutral 14.5 amps

ckt 8 15-2 amps (9 hid fixtures)
ckt 10 15.2A (10 hid fixtures)
ckt 12 6.7A (16 flur fxts)

I didn't install it, was done by a contractor prior to my working there, the contractor was called back once to fix it, but he just made it worse

oh , the pipe is uniformly hot at least fer the first 20 feet or so that i was able to feel...<G>

tajoch,

I would say that the heat is to be expected under the circumstances. 50% of 30 is 15A and you even have some over that.

If you can change these wires to #10s or remove half of them you should be Ok.

If you want to try an experiment take the bulbs out of 1 or 2 fixtures on each of the circuits and see what happens to the Temp of the conduit.

Bill

First I would use my Amprobe just to see if we have a bad connection which I'm sure you did. Next I would worry about the metal halides. Watts?
I used to warm up next to those things in the winter!

Bill A. another good answer in my opinion, I bet if he takes out just two halides on each circuit he will see a dramatic loss in temps on the high temp zone. But I still think it sounds like an bad conection prob. Hope he lets us know!

[This message has been edited by Resistor (edited 07-21-2001).]

>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.

>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).]

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).

>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?

..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?

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.

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?

>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.

>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.

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).]

>Wouldn't more heat be generated on each and every neutral conductor?
No. If you look at the numbers, two of the three neutrals (in multiwire) are carrying more than the most carried by any one UGC.

>Wouldn't each neutral be hotter carrying the c.15A loads?
No. Four would be hotter, three would be cooler. 5 out of 8 would be overloaded instead of 2 out of 3.


Circuit 7 & 9 is a fine example. That circuit is legal for the UGCs but the GC is overloaded. That's what can happen. That's why the neutral should be oversized.

>the "whopping 6 amps" that the 4 neuts carry?
You might want to re-read the numbers.
How did you determine that there are four neutrals carrying 6 amps each?

I'm not going to go another round of your dissect-word-by-word-"quote" & quip arguments.
You'd better call all of the switchgear manufacturers, maybe Lithonia or Cooper lighting (their modular systems don't have an upsized neut), and inform them of your brilliant findings.
Then go rewire all the 3Ø - 277/480 warehouses in the country. They really aren't done to your liking. I'm done on this thread.


(My apologies to the rest of you for my rudeness)


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

>You'd better call all of the switchgear manufacturers, maybe Lithonia or Cooper lighting (their modular systems don't have an upsized neut), and inform them of your brilliant findings.
Perhaps so.

>Then go rewire all the 3Ø - 277/480 warehouses in the country. They really aren't done to your liking.
Correct.

Joe Tedesco provided this link http://www.copper.org/pq/primer/ a while back.

Scott35 wrote on 02-04-2001 03:07 AM:
... older services / feeders and sub feeders; where in the past it was OK to derate the Grounded Conductor on 1 phase 3 wire systems, due to the fact that the currents would have balanced themselves out across the Ungrounded Conductors when the Transformer was delivering it's rated KVA for multiwire circuits.
This has been common in older Commercial installations - prior to circa 1985 or so - when the derating thing changed, not allowing derating for non-linear and/or high harmonic loads being the majority loads.
I am unsure of the exact year that this took place, nor if it applies to Residential installations.

The Three Phase 4 wire systems will have the dreaded "Triplen" Harmonic frequencies to deal with, where as the Single Phase systems will deal with "Beat" frequencies - much like how a Single Phase AC Motor's rotor [Secondary] is subjected to - Double frequeny pulsations.

There is a difference in the level of THD that causes trouble between the two systems.

For a Three Phase system, if the THD is at 33% or more per Line on a Line to Common 4 wire multiwire branch, this almost always doubles the current in the common conductor.

For a Single Phase system, if the THD is at 50% or more per line on a line to neutral 3 wire multiwire branch circuit, this almost always doubles the current in the neutral conductor.

Depending on what frequency is carrying the highest distortion, there may not be an equal frequency on the other Line to balance out, so it is an unbalanced current that flows in the neutral conductor - even if both the loads appear to be equal in current value and on opposite Lines [1 phase 3 wire - 120/240 VAC].
...
To sum it up: The THD [Total Harmonic Distortion] would need to exceed 50% on each Line where their is a common harmonic frequency, to cause double current flow in the neutral of the 120/240 VAC 1 phase 3 wire multiwire circuit.
If the harmonic is not common to each line, then the Double Frequency Pulsation problem will make the THD 25%, instead of 50%, to cause an overloaded neutral.

The 3 phase 4 wire multiwire circuit has the problem of "triplen" harmonics, which would be 3 times the fundamental, then 3 times the triplen frequencies after that [or Hz3].
So with a fundamental frequency of 60 Hz, these would fall into 180 Hz, 540 Hz, 1,620 Hz and on.
These overload the common conductor when the THD is or exceeds 33%.