determining size of residential service

[Stevenfyeager]

With some older residential service panels not having main breakers, how do you know the size in amps of the service? I can sometimes guess by looking at the size of the service drop conductors, or occasionally the utility company can tell me. Sometimes the drop conductors size is not accurate. How do you know? Thank you.

 

[1793]

Good question, in the past I've looked at the Water Ground conductor to help in determining the size of the Service.

 

[infinity]

IMO without a main you would use the service entrance conductors to determine the service size.

 

[Stevenfyeager]

IMO without a main you would use the service entrance conductors to determine the service size.

A lot of panel labels have long fallen off and gone. I can usually tell between 100 and 200 amp by drop conductors (although not always). But bet. 100 and 125 is harder. Is there any way by looking at the meter itself?

 

[growler]

A lot of panel labels have long fallen off and gone. I can usually tell between 100 and 200 amp by drop conductors (although not always). But bet. 100 and 125 is harder. Is there any way by looking at the meter itself?

Without the label I can't think of any way. Years ago a 100 amp would have had a 100 amp meter base and a 125 would have jumped to 200 amp meter base but now there are 100 amp services that use a 200 amp meter base ( works just fine). Some power companies don't care which you use if it not to small.

The service conductors will give an indiction but that panel did have rating of 100 or 125.

 

[GerryB]

With some older residential service panels not having main breakers, how do you know the size in amps of the service? I can sometimes guess by looking at the size of the service drop conductors, or occasionally the utility company can tell me. Sometimes the drop conductors size is not accurate. How do you know? Thank you.

Is this common in your area? Have never seen a residential main service without a main breaker (or fuses) either at the panel or the meter regardless of age around here. On multifamily services I have seen for example a 2 family with two 100 amp panels and overall just 150a coming in.

 

[user 100]

A lot of panel labels have long fallen off and gone. I can usually tell between 100 and 200 amp by drop conductors (although not always). Is there any way by looking at the meter itself?

I agree with the others about perusing the service conductors as being probably the best way to determine unknown ampacity of service. About the meter, if it's an old round base, most certainly the original service was 100 amps or less.

 

[pkelectrical]

Is this common in your area? Have never seen a residential main service without a main breaker (or fuses) either at the panel or the meter regardless of age around here. On multifamily services I have seen for example a 2 family with two 100 amp panels and overall just 150a coming in.

I didn't see that either. Although I did not work on that many old homes, oldest was from the year 1880, belong to historical society

 

[1793]

Is this common in your area? Have never seen a residential main service without a main breaker (or fuses) either at the panel or the meter regardless of age around here. On multifamily services I have seen for example a 2 family with two 100 amp panels and overall just 150a coming in.

In my area, YES, I see it quite a bit hence the problem getting an accurate Service size. Panels are usually split buss and conductors don't have any markings, visual size determination can be an issue and make it a little difficult.

 

[Stevenfyeager]

Thank you. I'm seeing it quite often. Ive had two this past week. Usually there is a 50 amp "general lighting load" breaker feeding the bottom half of the panel, but no main for the top. I wonder what keeps that half of panel from overloading if homeowners put too large of breakers in that section. ?

 

[kwired]

Thank you. I'm seeing it quite often. Ive had two this past week. Usually there is a 50 amp "general lighting load" breaker feeding the bottom half of the panel, but no main for the top. I wonder what keeps that half of panel from overloading if homeowners put too large of breakers in that section. ?

This is not limited to split bus panels. Any time you have permitted 2-6 mains, you only need to size the service conductors to the total calculated load.

Can be common to see something like a 4 apartment building with 100 amp service disconnect for each apt (a net of 400 amps of main breakers) yet only have 200, 250, 300 or something less then 400 amp service conductor because that is all the load calculation calls for.

 

[meternerd]

The utility would know, but a good bet is the meter. Newer services are seldom smaller than 200A if 240/120. These would have a FM 2S 240V 200A meter. Older 120V services would be FM 1S 120V 100A. My guess is that most utilities do not offer 100A services anymore. We don't. Network meters (two phases of a 208/120 three phase bank) would be FM 12S 120V 200A.

 

[iwire]

My guess is that most utilities do not offer 100A services anymore.

I would say your guess is far from correct.

 

[goldstar]

My guess is that most utilities do not offer 100A services anymore.

IMHO, it's not up to the POCO. If a house doesn't warrant a 150 or 200 amp service whomever is performing the installation makes the size determination based on load calculations.

Also, you can't assume that the service was done properly to begin with or that the breaker panel may have been improperly changed at some point prior to you getting there. I just looked at a service for one of my neighbors who just moved in in February. He has a brand new 150 amp, main breaker panel and I suspected something was not right. No inspection sticker (first clue), none of the breakers were labeled (second clue), original POCO crimps still on the triplex (third clue), 100 amp meter enclosure and original 100 amp SEU cable (4th clue) and the meter tag cut (final clue). I'll be correcting that service this week.

 

[Dennis Alwon]

We see the six-handle rule alot here back in the 70's and 80's but not as much anymore. Everyone I can remember was 200 amps however there were some split buss panels with fuses that may have been 150 amps or so. As others have stated the service conductors at the panel is the only way to be certain

 

[Stevenfyeager]

I agree with the others about perusing the service conductors as being probably the best way to determine unknown ampacity of service. About the meter, if it's an old round base, most certainly the original service was 100 amps or less.

So, is there an infinite amount of amps that can come into a house panel that has no main? There is no limiter of any kind in a meter ? Or is there an OCPD on the pole? Without main breaker like so many of these older panels, what keeps the panel from overloading when homeowners gradually add circuits and overload the panel rating? Thank you

 

[kwired]

So, is there an infinite amount of amps that can come into a house panel that has no main? There is no limiter of any kind in a meter ? Or is there an OCPD on the pole? Without main breaker like so many of these older panels, what keeps the panel from overloading when homeowners gradually add circuits and overload the panel rating? Thank you

Not a simple yes or no answer.

Many old homes never have a problem because the load just isn't there.

The main overcurrent device is there to protect the conductors more so then to justify size of the service.

Current is limited by the capacity of the supply at least to some extent, put 50 or 60 kVA of load on a 10 or 15 kVA transformer and chances are it will trip something at some point, it will ordinarily trip proper service overcurrent protection first though if talking about old undersized service

However keep adding load to an old house with 60 or 100 amp supply conductors that happens to be on a 75 or 100 kVA transformer (likely has other customers supplied as well) and you have nothing to keep from overloading those conductors if there isn't proper main(s) to protect them.

I am about to start working on an upgrade to a facility that will only have about 200 kVA of calculated load. POCO is going to provide a 225 kVA transformer, but my service equipment will be able to handle a little more then double that amount. If significant load is ever added POCO will likely need to upgrade their transformer.

 

[meternerd]

I think I mis-spoke....we charge a "facilities fee" when we supply a new service. The fee is the same for 200A or less. No advantage for 100A financially from the utility standpoint. We would likely use the same size service drop wires to reduce the inventory of smaller service wire. Transformers are usually shared between several customers so size is based on total expected load of all users. The VAST majority of customers opt for the 200A service because the cost of the meter panel is not much higher and we use a class 200 meter for ALL non-CT 120/240 services. I don't recall inspecting a new 100A service in years unless it was a 120/208 network setup in an apartment complex. Just my experience, though. As far as utility transformer protection, there is only primary fusing (or breaker for CSP) and it takes a TOTAL load to blow it, which is not likely to protect a single customer's service.

 

[kwired]

I don't recall inspecting a new 100A service in years unless it was a 120/208 network setup in an apartment complex. Just my experience, though. As far as utility transformer protection, there is only primary fusing (or breaker for CSP) and it takes a TOTAL load to blow it, which is not likely to protect a single customer's service.

Are you speaking just residential services? You likley have some non residential limited load services here and there that are only 30, 60 or 100 amp single phase don't you? You may still use a 200 amp meter in all of them though.

 

[meternerd]

Are you speaking just residential services? You likley have some non residential limited load services here and there that are only 30, 60 or 100 amp single phase don't you? You may still use a 200 amp meter in all of them though.

Not that I'm aware of. Non-residential requires test bypass type meter bases and rating is 200A. Above 200A is CT's. Not a lot of industrial loads up here, though. Bigger industrial get primary metering. Mostly ski resort type stuff such as hotels, restaurants, bars, etc. Been here 18 years and never hooked up anything less than 200A non-residential. Even sump pump, lighting, etc. get 200A. Probably due to our rate structure regarding 200A or less being the same fees. Probably not typical.