Ungrounded Delta breaker feeding Heater

[powerplay]

A freind was troubleshooting an 3 phase heater not working. It turned out one of the 3 "clips" on the panel bus had overheated on the push in Square D breaker(should have been an bolt on)....melted a bit of the bus away!

1) My thought was if it was an ungrounded Delta, is it possible a short was on one of the heater coils and drawing too much on one phase of the breaker?

2)If it was an existing ungrounded delta with a short on one phase, how do you meter it out?

3)I believe it was a 3 phase 4 wire system, but could bad bonding with a short on the one leg of the breaker for the heater have caused the "clip" on the bus to overheat and melt some of the bus? The breaker was moved, but i don't think they know what caused it yet...maybe a defective breaker? ...In defense of Square D, I know it could have been more than the 80% maunfacturers spec for warranty....will see if they checked the heater requirements.

Thanks again!

 

[augie47]

I don't think i've ever any correlation between "loose clip-buss damage" and the type of supply. It's a inherient problem with most all pug-on breakers.

 

[hurk27]

Heater loads have a way of finding the weak link in any electrical system, I just replaced a disconnect for a boost heater that was a Square D QO style plug on, same thing one of the connections on the breaker to the buss was burnt, the boost heater was only pulling 43.3 amps (9kw), and the disconnect was rated at 60 amps, but like I said, it only takes a slight loss of connection to start creating the heat at the connection and it will progress till it fails, the area was a high moisture environment (around the dishwasher) and just a little corrosion can start the whole heating process at the terminal, this is why I also do not like aluminum buss plug in breaker panels, especially installed in a high moisture environment like close to laundry equipment and some basements, or outdoors.

Also why I do not like space heaters unless they are on there own circuit/receptacle.

As far as thinking this has something to do with how the supply is wired, I don't see anything that would cause this kind of damage because an ungrounded delta had a fault to ground, because this would only make it a grounded delta, and loads would still see the same current, if a second fault would have occurred then it is possible that the current could increase but it should have tripped the OCPD, but would depend upon where in the element it faulted, a GF detector would have alerted to this fault, but most OCPD's would not trip until there rating is exceeded, a ungrounded delta should have GF alarms installed and is required by code.

 

[T.M.Haja Sahib]

Heater loads have a way of finding the weak link in any electrical system, I just replaced a disconnect for a boost heater that was a Square D QO style plug on, same thing one of the connections on the breaker to the buss was burnt, the boost heater was only pulling 43.3 amps (9kw), and the disconnect was rated at 60 amps, but like I said, it only takes a slight loss of connection to start creating the heat at the connection and it will progress till it fails, the area was a high moisture environment (around the dishwasher) and just a little corrosion can start the whole heating process at the terminal, this is why I also do not like aluminum buss plug in breaker panels, especially installed in a high moisture environment like close to laundry equipment and some basements, or outdoors.

Was everything listed for the application?

 

[powerplay]

When metering an ungrounded delta source to ground one would get unpredictable voltage readings, but it sounds like a short to ground wouldn't draw any current from this potential difference...say in one winding of the heater unless there is another fault on another phase? Does this mean that the one overheated clip on the back of the 3 phase breaker was probably due to normal current flow and a bad connection? Thanks again!

 

[jim dungar]

Does this mean that the one overheated clip on the back of the 3 phase breaker was probably due to normal current flow and a bad connection? Thanks again!

Yes, this is most likely.