Sub Panel Amperage Limit?

B

behindpropellers

Member
Location
NE Ohio
Occupation
Mechanical Engineer
Hello,

We have a 15KVA transformer that was installed for a 200A service. It previously had a 100A service that was installed directly to the panel in the building which was too small. I had an electrician install a sub-panel adjacent to the transformer and we ran the branches off of that. I asked him to install 200A service into the building.

After asking for the 200A service I was out at the jobsite a few days later and he had installed a 125A service.

Is there a technical reason to why they did not do what I asked them to do?

Other issues I am having with this contractor:

1. Main leg into panel was not torqued down.
2. Loose grounds in job box next to receptacle.
3. Ground rod was sticking out of the ground (hazard). I pounded it down and found the ground clamp was loose.
4. Electrician didn't tell me I needed a EE PE to sign off service changes prior to starting the job.
5. Panel installed has a manufacturing defect.

I'm frustrated that I hired an "expert" and I am now reading regulations to find out what they messed up.

Tim

PS - The conduit connecting panels is 2" PVC. 1/0 ALU conductors with a #4 AL ground.
 
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Your description leaves a lot to be desired however it might be worth noting the output of a 15kva transformer would be more in the 75 amp range and, although it might not be a violation to feed a 200 amp panel (dependent on primary protection), a smaller panel might be more logical which lklely explains why the electrician wanted a PE or EE involved.
Obviously there are several workmanship issues that need addressing
 
augie47 said:
Your description leaves a lot to be desired however it might be worth noting the output of a 15kva transformer would be more in the 75 amp range and, although it might not be a violation to feed a 200 amp panel (dependent on primary protection), a smaller panel might be more logical which lklely explains why the electrician wanted a PE or EE involved.
Obviously there are several workmanship issues that need addressing
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Thanks. The electrician did not get a PE involved, they just did the work. They inspector asked so I'm the one getting the PE involved.

Pretty frustrated with the whole thing.

Tim
 
behindpropellers said:
Rob,

Electric company transformer. 7.2KV/12.5KV.
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So I'm confused. Why does the size of the utility transformer matter? If you've upgraded from a 100 amp service to a 200 amp service it's up to the POCO to decide if the transformer is adequate and should have no bearing on what your electrician installed. It sounds like your issue is solely with your sparky that you're unhappy with.
 
infinity said:
So I'm confused. Why does the size of the utility transformer matter? If you've upgraded from a 100 amp service to a 200 amp service it's up to the POCO to decide if the transformer is adequate and should have no bearing on what your electrician installed. It sounds like your issue is solely with your sparky that you're unhappy with.
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According to the building inspector it matters.
 
Service transformer sizing and protection is the responsibility of the power company. The NEC and the building inspector have no control over them.

You are allowed to put in what ever size main breaker you want to, as long as you advise the power company.

If the meter socket and service were supposed to be upgraded to 200A, per job specs, your EC should have done so. No PE required. If the socket and conductors were not upgraded, 125A may be your maximum size.
 
After some digging:

The meter/breaker combo (exterior by our transformer) (SC2040M200C) has a branch breaker rating of 100A. My electrician installed a 125A breaker and 1/0 wire to my main panel.

Apparently the previous PN of this panel accommodated a 200A branch circuit and breaker.

I can't find a meter base/main breaker that is rated at 200A with a branch capacity of 200A. Any alternatives?

Tim
 
behindpropellers said:
After some digging:

The meter/breaker combo (exterior by our transformer) (SC2040M200C) has a branch breaker rating of 100A. My electrician installed a 125A breaker and 1/0 wire to my main panel.

Apparently the previous PN of this panel accommodated a 200A branch circuit and breaker.

I can't find a meter base/main breaker that is rated at 200A with a branch capacity of 200A. Any alternatives?

Tim
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Still not all that clear when you say "by our transformer" as to whether this is a utility transformer or not.

Utilities often have small transformers relative to the sum of all the main breakers it may end up supplying. They have no issue with overloading them to some extent as long as it is not for an extended time, but most those are not loaded all that much very often. I also see a lot of 200 amp services, particularly to dwellings that only have #2 or even # 4 aluminum service drop run to them. The load just isn't there and POCO isn't going to upgrade the drop until there is enough load to be worth updating it in their eyes. This is all ahead of the "service point" and NEC does not apply to it. POCO can sort of do whatever they wish with it as long as it will deliver proper voltage within certain tolerance level.
 
kwired said:
Still not all that clear when you say "by our transformer" as to whether this is a utility transformer or not.

Utilities often have small transformers relative to the sum of all the main breakers it may end up supplying. They have no issue with overloading them to some extent as long as it is not for an extended time, but most those are not loaded all that much very often. I also see a lot of 200 amp services, particularly to dwellings that only have #2 or even # 4 aluminum service drop run to them. The load just isn't there and POCO isn't going to upgrade the drop until there is enough load to be worth updating it in their eyes. This is all ahead of the "service point" and NEC does not apply to it. POCO can sort of do whatever they wish with it as long as it will deliver proper voltage within certain tolerance level.
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Hello,

The transformer is the utility transformer. The issue I am trying to resolve is getting 200A into the building where it is needed. The installed combo breaker/meter base only has a branch rating of 100A. It looks like I am going to need a dedicated outdoor main load center breaker installed and then follow that with additional panel to branch out of that supports a 200A branch circuit.

Tim
 
The part number and design of the SC2040M200C has been the same for ~30 years. Your electrician could have used the SC816D200C which has 200 sub feed lugs but not provisions for a 2nd 200 amp breaker. Don't really need the second breaker anyway. You would also only have 8 full sized spaces instead of 20.

Installing a separate panel off the current service panel will not gain you anything. You are still limited to feeding a 100 maximum. You can't feed a single 200 amp load.

Did your electrician know you required a 200 amp feed to the second building? If so I would put it back on them to install what you requested. If you didn't specify that you needed to run a 200 amp feeder off the new panel then its on you.

What else is connected to the service panel?
 
curt swartz said:
The part number and design of the SC2040M200C has been the same for ~30 years. Your electrician could have used the SC816D200C which has 200 sub feed lugs but not provisions for a 2nd 200 amp breaker. Don't really need the second breaker anyway. You would also only have 8 full sized spaces instead of 20.

Installing a separate panel off the current service panel will not gain you anything. You are still limited to feeding a 100 maximum. You can't feed a single 200 amp load.

Did your electrician know you required a 200 amp feed to the second building? If so I would put it back on them to install what you requested. If you didn't specify that you needed to run a 200 amp feeder off the new panel then its on you.

What else is connected to the service panel?
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Hi Curt.

Thank you for taking the time to answer.

There is a 15KVA transformer installed from the POCO. Previously it had a meter base on bollards that was feeding a 100A panel in the building 75 feet away with #4 Copper. The box had some water damage due to a leak in the roof and poor workmanship in the past.

I hired this electrician to inspect. He seemed very concerned with grounding a safety since the location is near water so I hired him.

When I talked with him I told him I originally wanted 200A into the building but the GC on the project told the electrician at the time to just put 100 because he thought we would never need it. Originally his plan was to install a meter/breaker combo box and replace the panel and clean up the conduit. I verbally told him to upgrade the service in the building to 200A and that I understood it would require pulling new wire into the building from the meter location. When I stopped out a few days later he had pulled new wire for 125 amps into the building. I would have never suggested pulling new wire for an extra 25A.

The meter service panel also powers a small shed 15 feet from the combo box. Originally, I was intending to power the shed from the panel inside of the building and still have the unused conduit installed.

From what you have written it sounds like I need to install the meter base, run 4/0AL into the building so I have 200A inside and then do my branch circuits from there.

Tim
 
If you want 200 amp supply conductors and panelboard that is certainly doable.

POCO is likely not going to be all that willing to put in a larger transformer if the load isn't there.

Typical residential service that does not have electric heat seldom ever sees high enough demand go over what a 100 amp supply will handle. You possibly may have short time peaks that push the limit but generally doesn't last long enough to push the 100 amp main breaker very far into a trip curve.

Other than houses with electric heat, I've seldom measured over 60-70 amps on a 200 amp main supply and quite often do not even get a measurement that high.
 
In my area the utility company transformers are undersized when they feed several services. They do not follow the NEC. I jnstalled a 800 amp service where they local utility company refused to either up size the existing transformer that feed a 200 & a 600 amp service.or better yet have it on its own transformer. Appeared to only be a 75 KVA transformer which is only goid for around 181 amps @ 240 volts three phase. Yep 1,600 amps of services on a 181 amp transformer. Told me that's be its out in the open and air cooled and can handle a lot more load. The 800 amp service was for a shop that ran 24/6 and load was over 600 amps. Original transformer burnt out within a month and exact replacement size transformer did not last 6 months. As far as 125 amp service if the transformer is owned by the utility company you should be safe if you apply for a service agreement form telling them you would like to increase the existing g 100 amp service to 200 amps. I would make sure a permit is pulled and inspected. The existing meter socket that electrician used for the 125 amp service should be rated for 200 amps. I only did maybe two 150 amp services over the years because a panel with a 200 amp main breaker is the same price as a 150 amp. Only a small! amount of money for larger wire. Labor is the same. When customers asked for a 150 amp service I would tell them for a little extra I would install a 200 amp.
 
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