1200 amp 208 volt main breaker tripped

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Fordean

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New Jersey
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Electrical Contractor
Had a 1200 amp 3 phase Sq D Main trip for a complex. 24 - 125 amp 1ph services and 1 - 400 amp house panel 3 phase.

Breaker would not clear on first attempt. Had to shut down all breakers and I think it cleared it but cant figure out why it tripped. To reset a 1200 amp 3 phase

Note I took apart and removed all meters to inspect, Due to the shearbolts not broken off. Checking for other flaws found none.

Is this normal procedure to shut down all main. Wasn't I inspected the whole cabinet. 1 screw in meter stack may have rubbed thru but no evidence of arc flash.

Question 1 Not sure if screw penetrated. But after all breakers were shut off. I was able to reset 1200 amp main. Then gradually restore in sequences of 4. Until all 25 were engaged. All was good. Did I need to shut off all breakers to reset this type of breaker?

Question 2 Shearbolts in meter stack. Whomever installed this service did not break off the shearbolt. Problem it can cause. I did not attempt to do this unless owner seen and asked to do so. Overall work looked ok from whomever installed. But this was red flag.
What can a non shearbolt do.. I did not check torque, Been on for 3 years plus.

Question 3. 400 amp 3 phase 208 main for house panel in busbar tap. They paralleled 2 - sets of 250 KCM alumin. But problem is they installed in 1 -4in conduit. Instead of separate Paralleled conduits.
Can the Increase of Magnetics (Ripple effect) Trigger this breaker to open.?

Question 4 It was in the blizzard. And all were home. Electric dryers., Gas stove. Electric water heaters. Could everyone have been stuck in home and used the dryer and washers with water heat demand. And exceed the Diversity of the load calcs? Any comments ?
 
A. It is always good policy to shut off all loads before resetting a main of that size. You did not mention the heat load, is it gas? Or electric? Heat pump? The emergency heat load would be substantial if it was a heat pump.
 
Question 3 that is a common wiring method and allowed by NEC. Ripple effect is not a term I am familiar with, and the magnetic fields cancel with the wiring method used.
Suggest you have a thermography done of the service and feeders when under a load, and take amp/volt readings. Per your Q2 you could have a loose connection, creating heat, causing your main breaker to trip.
Or the heavy load caused low system voltage
That breaker tripped for a reason.
 
It was likely the demand of everything being on at once during the blizzard. What time of day did it trip? Around 7 to 7:30am? That would be when the demand is highest during cold weather; everyone getting up and turning up their heat, making breakfast, taking showers. Evening around 6pm is another peak time, especially if that's when the wind was strongest, blowing the cold air into the apartments.

Add up the kW required for all that and I bet you come up with well over the service capacity.
 
Also Forgot to mention. The Engineers are specing 4 - 600 mcm to feed 400 amp 3phase subpanels.
Problem is the Mains , Can't accept a 600mcm. People are noticing after shipping and arriving to jobsite. S
I see this here on this situation. They ran 1 -4 inch conduit and now put 8- 250 kcm in one conduit, Instead of separate parallel conduits. Comment above says (Tom Baker) says this is ok to put two parallels in 1 conduit. I need a Code Page to view to confirm this. I never seen this on any drawings.
 
Fordean said:
Also Forgot to mention. The Engineers are specing 4 - 600 mcm to feed 400 amp 3phase subpanels.
Problem is the Mains , Can't accept a 600mcm. People are noticing after shipping and arriving to jobsite. S
I see this here on this situation. They ran 1 -4 inch conduit and now put 8- 250 kcm in one conduit, Instead of separate parallel conduits. Comment above says (Tom Baker) says this is ok to put two parallels in 1 conduit. I need a Code Page to view to confirm this. I never seen this on any drawings.
Click to expand...

Nothing in the NEC prohibits parallel conductors in the same raceway (as long as all of them are in there) but you need to take possible derating into account.
 
Fordean said:
Also Forgot to mention. The Engineers are specing 4 - 600 mcm to feed 400 amp 3phase subpanels.
Problem is the Mains , Can't accept a 600mcm. People are noticing after shipping and arriving to jobsite. S
I see this here on this situation. They ran 1 -4 inch conduit and now put 8- 250 kcm in one conduit, Instead of separate parallel conduits. Comment above says (Tom Baker) says this is ok to put two parallels in 1 conduit. I need a Code Page to view to confirm this. I never seen this on any drawings.
Click to expand...
They have to be ordered with the 600kcmil lugs, or the lugs changed out. But that is mute at this point, since parallels were ran instead.
 
Fordean said:
Also Forgot to mention. The Engineers are specing 4 - 600 mcm to feed 400 amp 3phase subpanels.
Problem is the Mains , Can't accept a 600mcm. People are noticing after shipping and arriving to jobsite. S
I see this here on this situation. They ran 1 -4 inch conduit and now put 8- 250 kcm in one conduit, Instead of separate parallel conduits. Comment above says (Tom Baker) says this is ok to put two parallels in 1 conduit. I need a Code Page to view to confirm this. I never seen this on any drawings.
Click to expand...
As noted, there is nothing in the NEC to prohibit parallel conductors in the same conduit. For Code references: 3101.0(H) discusses parallel conductors and 250.122(F) addresses grounding when paralleled in the same conduit
 
GF would be required on a 1200A service.

When you have a service 1000A or over, the Main must have GF protection, in which case it SHOULD also get a "Coordination Study" done with all of the other breakers down stream. Why? To avoid THIS EXACT THING.

If not properly coordinated, you can end up with a relatively minor fault event on a feeder or branch device down stream that is enough to cause the 1200A main to trip before that feeder or branch device reacts. A Coordination Study would be used to look at the trip curves of all of the downstream breakers and use that to determine the setting of the trips on the Main so that a fault is cleared at the CLOSEST device to the fault.
 
Classic “breaker tripped” issue. First mistake was just resetting without doing anything else. In US that’s an OSHA regulation…MUST determine source first. Also almost all of these breakers require inspection after tripping. On large breakers like that UL only tests around 25-50 times. Is this the first or last trip? The inspection takes seconds.

Normal procedure is that before just closing it back in if you don’t find anything then it’s downstream and with an apartment complex sort of impractical to find it easily. Open all the feeder breakers first THEN reset then turn on one at a time to try to narrow down where the problem is. Often I’ve seen cases on older breakers where the feeder is shot so the most minor short trips the main.
 
Fordean said:
Also Forgot to mention. The Engineers are specing 4 - 600 mcm to feed 400 amp 3phase subpanels.
Problem is the Mains , Can't accept a 600mcm. People are noticing after shipping and arriving to jobsite. S
I see this here on this situation. They ran 1 -4 inch conduit and now put 8- 250 kcm in one conduit, Instead of separate parallel conduits. Comment above says (Tom Baker) says this is ok to put two parallels in 1 conduit. I need a Code Page to view to confirm this. I never seen this on any drawings.
Click to expand...
Mac adapts
 
Jraef said:
GF would be required on a 1200A service.

When you have a service 1000A or over, the Main must have GF protection, in which case it SHOULD also get a "Coordination Study" done with all of the other breakers down stream. Why? To avoid THIS EXACT THING.

If not properly coordinated, you can end up with a relatively minor fault event on a feeder or branch device down stream that is enough to cause the 1200A main to trip before that feeder or branch device reacts. A Coordination Study would be used to look at the trip curves of all of the downstream breakers and use that to determine the setting of the trips on the Main so that a fault is cleared at the CLOSEST device to the fault.
Click to expand...
paulengr said:
Classic “breaker tripped” issue. First mistake was just resetting without doing anything else. In US that’s an OSHA regulation…MUST determine source first. Also almost all of these breakers require inspection after tripping. On large breakers like that UL only tests around 25-50 times. Is this the first or last trip? The inspection takes seconds.

Normal procedure is that before just closing it back in if you don’t find anything then it’s downstream and with an apartment complex sort of impractical to find it easily. Open all the feeder breakers first THEN reset then turn on one at a time to try to narrow down where the problem is. Often I’ve seen cases on older breakers where the feeder is shot so the most minor short trips the main.
Click to expand...
Personally I believe its a litte under sized
Engineering calc load 1089amps @ 208 3ph
Breaker setting seems to be dialed in at full 1200 amps at .5 sec.
Things found were
1. Plastic red separators on shear bolts were still in place. In meter stack busbar They never sheared/torqued bolts. Instead used deep socket to go over both. We have to check all services now
2. They ran a 400 amp Subfeed to house panel. 2 sets of paralleled 250 kcm in one 4 in pvc
We heard elevator guy argued about a ground issue, with orginal electrician
I guess elevator sensed a no ground issue. And locked out. Made me wunder
I opened 400 amp main subfeed disconnect off off 1200 amp busbar. To see
I found the ground wire In disconnect Looked slacked not tight to pulled 250's
So i opened 4 in LB and seen no ground in it
I got curious Why ir wasnt in LB this was 100 feet away
What i did notice is a hole drilled into LB
They banged a ground rod in and drilled a hole in LB to make it look like ground was parralleled
I went back to main, And wundered about slacked ground i seen previously
Told my guy watch this and he videoed disconnect As we priceeded
i told him that i think they forgot ground when they pulled 400 amp subfeed He didnt belueve me, So as he videoed me I tried pulling ground out of conduit To see if they cheated for inspection and just stuffed ground in piped for a couple feet
Sure enough As he videoed me I pulled 5 feet out Ground was severed and just stuuffed in pipe To obtain inspection
Going back to LB Thats why they banged ground rod
 
Wow so all that 400A house panel had was the earth as a EGC?
You might check voltage drop under full load at a peak time the W/ POCO present, sometimes they can 'notch up' the transformer changer taps, that would drop the amps some.
 
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