What happens when a main panel is overloaded?

[fandi]

Hello All,
Many years ago, an electrical system for an apartment was designed with not much spare capacity (for the main service). Now one unit at a time adds an EV charger (32A) to that unit's load. A load calculation per section 220 was performed each time an EV charger is added to a unit to show that it's OK to add 32A to that unit's sub-panel. First few EV charger additions were OK until one EV charger make the main service overloaded. My question is what will happen if the main service panel is overloaded? If the main service panel is placed inside the apartment, would the place catch on fire because of wires being overheated?
Thanks.

 

[Hv&Lv]

Wait, you can move your main panel to another location??
if your breaker is sized correcty, it should trip before any wire gets that hot

 

[fandi]

Wait, you can move your main panel to another location??
if your breaker is sized correcty, it should trip before any wire gets that hot

The main panel can't move to another location. I agree with you that the breakers are supposedly trip to protect the wires. So basically if the main service panel is overloaded, the main breaker simply trips and the whole apartment will be without power but nothing dangerous would happen?

 

[kwired]

The main panel can't move to another location. I agree with you that the breakers are supposedly trip to protect the wires. So basically if the main service panel is overloaded, the main breaker simply trips and the whole apartment will be without power but nothing dangerous would happen?

Presuming the main breaker functions properly, yes.

 

[fandi]

I have seen in the field some breakers too old that they don't trip to protect the wires. Some trip half way (not on, not off). But I guess if anything bad happened, it's on the apartment owner for not replacing the ancient electrical system.

 

[kwired]

I have seen in the field some breakers too old that they don't trip to protect the wires. Some trip half way (not on, not off). But I guess if anything bad happened, it's on the apartment owner for not replacing the ancient electrical system.

Majority of miniature/molded case circuit breakers out there trip and the handle goes to a midway position, you must move it all the way to the off position to reset it then turn it on again to close the circuit.

 

[PaulMmn]

Majority of miniature/molded case circuit breakers out there trip and the handle goes to a midway position, you must move it all the way to the off position to reset it then turn it on again to close the circuit.

I think Fandi is referring to an -old- breaker that doesn't trip properly-- maybe half-way off, with the contacts still engaged.

 

[kwired]

I think Fandi is referring to an -old- breaker that doesn't trip properly-- maybe half-way off, with the contacts still engaged.

Maybe. Seen very few if any that will not open. Usually if there is problem because of age or other deterioration they fail to close again, but I won't claim it is impossible either.

 

[electrofelon]

Your description of the electrical system is not very clear, but I assume you have a main breaker and if so then yes that would trip. If you had a service with multiple service disconnects, then typically the sum of the main breakers exceeds the ampacity of the service conductors and panel board or switchboard, so indeed you could theoretically get into a meltdown if things got real bad. Due to diversity and the conservative nature of NEC calcs, It would take a lot to get into an overload situation.

 

[kwired]

Your description of the electrical system is not very clear, but I assume you have a main breaker and if so then yes that would trip. If you had a service with multiple service disconnects, then typically the sum of the main breakers exceeds the ampacity of the service conductors and panel board or switchboard, so indeed you could theoretically get into a meltdown if things got real bad. Due to diversity and the conservative nature of NEC calcs, It would take a lot to get into an overload situation.

Some those cases with multiple mains you may trip POCO protection before you overload the main conductor for too long, just depends on setup and POCO design practices. Maybe you have 1000 amp worth of overcurrent devices, but actual load of only 400 amps, chances are POCO only has a transformer with ~ 400 amp output rating if the load isn't expected to exceed that.

 

[Jraef]

I'm a bit confused over your use of "main panel" here. If it is the Main Panel for the entire complex, as you seemed to indicate at first, and the Main Breaker in that panel trips, you would lose power to ALL of the apartments served by that panel.

Someone may need to consider beefing up the service, or having another service drop put in just for the EV chargers.

 

[jaggedben]

Your description of the electrical system is not very clear, but I assume you have a main breaker and if so then yes that would trip. If you had a service with multiple service disconnects, then typically the sum of the main breakers exceeds the ampacity of the service conductors and panel board or switchboard, so indeed you could theoretically get into a meltdown if things got real bad. Due to diversity and the conservative nature of NEC calcs, It would take a lot to get into an overload situation.

This. Is there a main breaker for the whole service or just one for each unit?

If the latter, my guess is probably nothing too bad would happen, there's a lot of extra safety factor built into the NEC. But if something bad happened (melted wires or bussing) then whoever didn't do a proper load calculation on the critical EV charger would have a lot of liability on them.

 

[fandi]

This. Is there a main breaker for the whole service or just one for each unit?

If the latter, my guess is probably nothing too bad would happen, there's a lot of extra safety factor built into the NEC. But if something bad happened (melted wires or bussing) then whoever didn't do a proper load calculation on the critical EV charger would have a lot of liability on them.

This is a hypothetical question so there could be a main breaker, or not depends on the situation. First few electricians installed the EV chargers without problems. Then there's one poor electrician installed one EV charger that caused the entire apartment overload, even he did the load calculation for the unit he's working on and the numbers are fine. I think the problem is all the electricians working at that apartment only performs each unit's load calculation. None bothers to care about the main service.

 

[kwired]

This is a hypothetical question so there could be a main breaker, or not depends on the situation. First few electricians installed the EV chargers without problems. Then there's one poor electrician installed one EV charger that caused the entire apartment overload, even he did the load calculation for the unit he's working on and the numbers are fine. I think the problem is all the electricians working at that apartment only performs each unit's load calculation. None bothers to care about the main service.

load diversity on dwellings, especially when you have multiple ones served by common supply is low enough that you can get away with a lot, even when NEC says you need more. What gets you into trouble the most is electric heat, but you may get away with a little more of that in the south then you will in the north. But there still is a point where you can have too much added or some occupants may typically use more than others and get into overloading situation easier.

 

[ptonsparky]

The buss and service conductors to a panel with six mains could conceivably be overloaded by those additions.

 

[GoldDigger]

I think Fandi is referring to an -old- breaker that doesn't trip properly-- maybe half-way off, with the contacts still engaged.

Or a two pole breaker that does not open both sides.
Usually the handle still goes to the TRIP position even when the contacts stick.