Need help diagnosing a panel issue.

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Coppersmith

Coppersmith

Senior Member
Location
Tampa, FL, USA
Occupation
Electrical Contractor
panel2.jpg

A few days ago I did a service call here. There is a smoky smell in this panel. Nothing (including the main) feels warm. I removed all the branch breakers and inspected the breakers and the bus. The only damage I could find was under a two-pole twin (4th and 5th breaker on left side) where a plastic fin on the bus was melted. That 20 amp breaker is connected to a 18.75 amp water heater. I replaced the breaker and relocated it to a spot with more air circulation.

The panel is in a closet. I closed the door and turned off the light. It was pitch black in there. I could see no arcing or flame. I found no terminations that were loose.

Last night the client was watching TV in bed so I suspect there was a light total load. The 150 amp main breaker tripped. I'm at a loss as to what could be causing the issue. I'm thinking there is a main breaker failure of some sort, but like I said the breaker was cool to touch when I last checked.

I'm heading over there soon. I'm hesitant to change the main without knowing the cause. Please give me suggestions, Thanks.
 
I would megger test the buss in the panel first. 18.75 amp load is too high for a 20 amp circuit also.
 
In no particular order:

Electric heat uses a lot of current; longer at night.

Check main (all) breaker terminals for tightness.

Wires and buses can conduct heat into breakers.

Replace 20a breaker with 30a (if wire size allows).

Inspect breaker bus stabs and breaker contacts.

Rearrange breakers so 2p breakers don't share stabs.
 
I would also perform a fall-of-potential on the main. Poor contact could produce the effects you note.
 
acrwc10 said:
I would megger test the buss in the panel first. 18.75 amp load is too high for a 20 amp circuit also.
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I agree it's too high, but the cable is 12ga so I can't put a larger breaker in. This is a manufactured home so cable is inaccessible. Client has limited funds, so I can't run a 10ga cable. I don't think this is the source of the main trip problem.
 
Is that panel in a mobile home? (trailer) The paneling & trim leads me to think so. What is the dark spot on to of the box, to the left of the bends in the feeder conductors? The main tripping makes me wonder if there is a loose connection somewhere.
 
norcal said:
Is that panel in a mobile home? (trailer) The paneling & trim leads me to think so. What is the dark spot on to of the box, to the left of the bends in the feeder conductors? The main tripping makes me wonder if there is a loose connection somewhere.
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It's a manufactured home. I hadn't noticed the dark spot before, but it's right over the main. Perhaps it's smoke that settled there from something simmering in the main.
 
Is it safe to turn the main back on? Any arc flash potential? If it's a loose connection I'm fine, but what if something inside is messed up?
 
norcal said:
What is the dark spot on to of the box, to the left of the bends in the feeder conductors? The main tripping makes me wonder if there is a loose connection somewhere.
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It looks like the right terminal on the main breaker has overheated, probably due to a bad connection with the aluminum service conductor. If so, that could explain the main breaker tripping, the whitish deposits on the other conductor above it, and the dark spot mentioned on top of the panel.
 
It may not be the only issue, but you had a partially melted breaker for the water heater. And, the water heater element is oversized for the wire. They do make 240V lower wattage elements for water heaters.
 
tthh said:
It may not be the only issue, but you had a partially melted breaker for the water heater. And, the water heater element is oversized for the wire. They do make 240V lower wattage elements for water heaters.
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The breaker was not melted. There was not any visible damage to the breaker, just to the plastic fin on the bus that sits between the two poles. I replaced the breaker out of an abundance of caution.
 
synchro said:
It looks like the right terminal on the main breaker has overheated, probably due to a bad connection with the aluminum service conductor. If so, that could explain the main breaker tripping, the whitish deposits on the other conductor above it, and the dark spot mentioned on top of the panel.
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I tugged on the feeder conductors and nothing was loose. I'll try tightening the top and bottom connections with a tool to verify.
 
tthh said:
It may not be the only issue, but you had a partially melted breaker for the water heater. And, the water heater element is oversized for the wire. They do make 240V lower wattage elements for water heaters.
Click to expand...
If there is a further issue with the water heater breaker I will suggest using a lower wattage element.
 
Perhaps the service conductor on the right wasn't fully inserted into the breaker terminal because part of the wire insulation is sticking out and it's preventing the wire from being pushed in all the way. I mention this because the stripping of the insulation is uneven, and a significant part of the the bare conductor is visible.
 
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