Utility KWH meter overload tolerance

[jtester]

Our local utility just threw a new twist in designing electric services. They rejected a 200 amp service with a 200 amp meter and a panel having a 200 amp main breaker serving as a service disconnect because the panel board bus is rated for 225 amps. They believe someone will change out the 200 amp main breaker to a 225 amp breaker and overload their meter. They have a similar rule for their 320 amp meter, but that is really messy since panel busses are rated 400 amps, and fusible disconnects in the 400 amp class can accept up to 400 amp fuses. I don't know of any that stop at 300 amps.
I have always believed that utility meters can withstand as much as 100% overload, but I can't find any good information on that subject. I hope to discuss this issue with the utility, but would like to know if their overcurrent protection efforts are appropriate and even common.
Thanks in advance for any information or opinions you might have.
Jim T

 

[GoldDigger]

Our local utility just threw a new twist in designing electric services. They rejected a 200 amp service with a 200 amp meter and a panel having a 200 amp main breaker serving as a service disconnect because the panel board bus is rated for 225 amps. They believe someone will change out the 200 amp main breaker to a 225 amp breaker and overload their meter. They have a similar rule for their 320 amp meter, but that is really messy since panel busses are rated 400 amps, and fusible disconnects in the 400 amp class can accept up to 400 amp fuses. I don't know of any that stop at 300 amps.
I have always believed that utility meters can withstand as much as 100% overload, but I can't find any good information on that subject. I hope to discuss this issue with the utility, but would like to know if their overcurrent protection efforts are appropriate and even common.
Thanks in advance for any information or opinions you might have.
Jim T

Search the forum for discussions of meter ratings in terms of continuous, etc.
Also, for some purposes such as connecting a solar generating system, it is sometimes essential that the bus be rated higher than the main breaker.
I think that somebody at the utility has gone off the deep end on this one, but I am not sure how to bring them back to reality.
100Amp panels for a 100A service often have a 125A bus, but the panel may still be rated for just 100A.
I can see some small justification for concern on their part if the panel in question is rated/labelled as a 225A panel. But often the manufacturer will just rate the panel for 200, with a max breaker size of 200, but use 225A bus bars for their own business reasons.

 

[Hv&Lv]

I have read that the old class 200 mechanical meters were designed to handle four times the overload, I think it was an old military book that is online and dates back to the late 80's or early 90's. I can't remember how to find it again right now.

 

[GoldDigger]

I have read that the old class 200 mechanical meters were designed to handle four times the overload, I think it was an old military book that is online and dates back to the late 80's or early 90's. I can't remember how to find it again right now.

From what I have heard anecdotally about smart meters, they may be worried about overloading the built-in contactor rather than the power measurement side.

 

[kwired]

If someone is going to change that main breaker, aren't they likely going to call POCO to pull meter or deenergize in some way? At that time they can then respond however they feel appropriate to changing the breaker:slaphead:

There is also the issue of the service conductors not being large enough should someone change the main from 200 to 225 but apparently all they care about is the meter itself.

 

[Hv&Lv]

From what I have heard anecdotally about smart meters, they may be worried about overloading the built-in contactor rather than the power measurement side.

Good point. Still, I have never seen a class 200 pull 200 amps for long. If that were the case the entire service would be sized larger to account for connected load, correct? I know when I do a calculation for a service the service is sized for about all the items to be used at the same time, and we all know in the real world that seldom happens.
I agree with some others that the utility is being anal on this one.

 

[kwired]

Good point. Still, I have never seen a class 200 pull 200 amps for long. If that were the case the entire service would be sized larger to account for connected load, correct? I know when I do a calculation for a service the service is sized for about all the items to be used at the same time, and we all know in the real world that seldom happens.
I agree with some others that the utility is being anal on this one.

Am currently working on figuring out exactly what service upgrades to do at a school building that will be installing new HVAC system and adding a new chiller unit which will be a significant load in addition to what is existing. Current service is single phase with multiple disconnecting means so the main service conductors are sized by load more so than by overcurrent devices.

It is supplied by a 100kVA transformer and 350 copper conductors for the lateral, though there is about 800 amps worth of overcurrent devices supplied by those conductors. Check with POCO records on past peak demand shows it was only about 39kVA, which is only around half of what things are designed for, and just doing some fairly quick calc's according to art 220 says we should be closer to the 100kVA level.

 

[mivey]

I have always believed that utility meters can withstand as much as 100% overload, but I can't find any good information on that subject.

Depends on the duration. They can withstand faults of about 12,000 amps for a few cycles. Many can withstand a 20% overload for several hours, or 100% overload for 0.5-1.0 seconds.

The tests only require they be able to carry 100% of the maximum load continuously without damage or overheating. For a class 200 meter the maximum continuous current would be 200 amps or 666.7% of 30 amps. Ambient temperature can make some difference.

 

[mivey]

I can see some small justification for concern on their part if the panel in question is rated/labelled as a 225A panel.

Maybe. I doubt that even if they put in a 225 amp breaker that it would be carrying 200 amps continuously. I think the POCO is being a bit too "by the book" in this case.

 

[Sierrasparky]

Maybe. I doubt that even if they put in a 225 amp breaker that it would be carrying 200 amps continuously. I think the POCO is being a bit too "by the book" in this case.

It's all about those crappy smart meters. They cannot handle the load. Look at most of the meter/main combos the meter socket is only rated at 160 amps continuos.

Those meters are a bunch of crap and will continue to cause problems