Hot spot scanning of breaker enclosure

[Tainted]

I was scanning for hotspot on a standalone 100 amp breaker enclosure feeding an apartment. The neutral/lug was the hottest thing in the enclosure reading at 94.6F, the temperature of the phases were less than the neutral. Is this normal? Could it just be phase imbalance? or improper connection?
I think most lugs are good for 75C (167F) so would this be normal?

 

[LarryFine]

It looks like it's hottest at the add-on lug.

I would move the upper neutral wire to the top lug, and the lower neutral wire to the bottom lug.

 

[petersonra]

95 deg f is not hot enough to worry about imo.

 

[ptonsparky]

I would investigate. Do a FOP. Check torque. Remove clean and reinstall. Check amps.
Is this a neutral from a 208 wye transformer bank?

 

[Tainted]

I would investigate. Do a FOP. Check torque. Remove clean and reinstall. Check amps.
Is this a neutral from a 208 wye transformer bank?

Sorry, but how would doing FOP be beneficial? Neutral is taken from a 208V wye system if that helps

 

[Tainted]

95 deg f is not hot enough to worry about imo.

how many degrees would be hot enough?

 

[synchro]

95 deg f is not hot enough to worry about imo.

And based on the scale on the right the neutral lug is only about 6 degrees F above that of the enclosure. So not very much, although more than on the phase conductors.

I would investigate. Do a FOP. Check torque. Remove clean and reinstall. Check amps.
Is this a neutral from a 208 wye transformer bank?

Sorry, but how would doing FOP be beneficial?

I think ptonsparky might have meant to check the voltage drop between the input and output wires going to the neutral buss? If you can put meter probes on the wire conductors themselves without contacting the lugs, then that would give the best measurement of the voltage drop.

Neutral is taken from a 208V wye system if that helps

The neutral will conduct the same amount of current as balanced L-N loads placed on 2 phases of a 208V wye system, and so significant neutral current is expected. However, it would be best to measure the currents as was noted above.

 

[LarryFine]

95 deg f is not hot enough to worry about imo.

Not yet, but warm connections usually become warmer connections over time.

 

[LarryFine]

Sorry, but how would doing FOP be beneficial?

To uncover voltages between points where there should be no voltage difference.

 

[Tainted]

To uncover voltages between points where there should be no voltage difference.

so what I would do is put a voltmeter on the line side and load side of neutral lug? what value of the voltage drop would be concerning?

 

[LarryFine]

so what I would do is put a voltmeter on the line side and load side of neutral lug? what value of the voltage drop would be concerning?

Yes. It's a troubleshooting method, useful for testing breakers, switches, contactors, etc.

The value is in narrowing down the location of the resistive contact point to remedy it.

Knowing the exact voltage drop, which varies with load, is not particularly important.

 

[Tainted]

Narrowing down the location of the resistive contact point to remedy it.

Knowing the exact voltage across the joint is not particularly important.

Good point.

Now before I recommend the building an electrician to investigate this, the ultimate question would be if it is really necessary fixing this. I don't want to be accused of fixing something that's not broken.

 

[LarryFine]

Let me answer you this way: Every termination and connection I make, from a fixture wire on a #14 wire to the largest power terminals, I consciously say to myself:

"This connection will not be the one that weakens or fails."

That means I make sure the wire-nut grabs all wires properly, the set-screw is tight after the strands spread out, there is good metal-to-metal contact, no undue stress, etc.

To me, there is no good reason to leave a known weak connection. Heat is the main by-product of a poor connection, and tends to make the connection weaker over time.

"Holy snowballing effect, Batman!"

 

[ptonsparky]

It may not be necessary, but how will you know?
Is the neutral smaller than the phase conductors? That may be enough to account for temp difference. We can't tell from here. Moving them as suggested may cure it. Maybe not.

 

[LarryFine]

Moving them as suggested may cure it. Maybe not.

<---- Not always right, but never in doubt.


The neutral conductors do not need to follow the line-on-top/load-on-bottom configuration.

 

[Tainted]

Let me answer you this way: Every termination and connection I make, from a fixture wire on a #14 wire to the largest power terminals, I consciously say to myself:

"This connection will not be the one that weakens or fails."

That means I make sure the wire-nut grabs all wires properly, the set-screw is tight after the strands spread out, there is good metal-to-metal contact, no undue stress, etc.

To me, there is no good reason to leave a known weak connection. Heat is the main by-product of a poor connection, and tends to make the connection weaker over time.

"Holy snowballing effect, Batman!"

I get it. I think the short answer here is "better safe than sorry" lol

 

[electrofelon]

Is the neutral smaller than the phase conductors?

I had the same thought. If it's a reduced neutral, and since it's two legs of a wye system, that could explain the higher temp.

 

[ptonsparky]

<---- Not always right, but never in doubt.


The neutral conductors do not need to follow the line-on-top/load-on-bottom configuration.

Referring to just the act of installing them again with assumed correct torque. Top/bottom, left/right doesn't matter.

 

[Tainted]

I had the same thought. If it's a reduced neutral, and since it's two legs of a wye system, that could explain the higher temp.

oh right because it doesn't necessary cancel them out as it would with a single transformer center tap neutral.

Not sure if the neutral is reduced though

 

[LarryFine]

Referring to just the act of installing them again with assumed correct torque. Top/bottom, left/right doesn't matter.

I was only referring to the fact that the bottom wire won't reach the top lug.

My guess is that that's why the (un-needed) accessory lug was added.

Each could have been landed on the closer lug. I'm suggesting doing that now.