100 amp breaker in 200 amp panel

[Cow]

More often then not 200 amp panels have many more breaker spaces available than a 100 amp panel. If I bought a main lug 200 amp panel just for the extra breaker spaces and then installed a backfed 100 amp breaker as the main, it's ridiculous to think you'd deny service just because the panel has a 200 amp bus rating.

 

[GoldDigger]

It may be ridiculous, but a good number of POCOs, notably Los Angeles DWP, are firmly committed to it and are not open to logic. In particular if you upsize the panel bus to allow you to satisfy the 120% rule, they will insist that you also pay whatever it may cost for a service upgrade. Even though you are actually decreasing the load rather than just keeping it the same.

Tapatalk!

 

[ActionDave]

I find this debate quite interesting since most residential services are grossly oversized using NEC calculations compared to what they draw in the real world. Power company logs of actual usage prove this.

 

[kwired]

Of course we'd reconnect his service, but we'd upsize the service drop wires if necessary and charge him for the cost based on the panel rating. If he had a 100A service and decided to spend the extra money for a 200A panel, when we came to reconnect the new panel, we would not continue to consider it a 100A service, even if he had a 100A main. We would assume he'll eventually increase load. We call it "demand capability". Why else would he fork over the extra dough for a bigger panel and wire? That's assuming he asked for a disconnect. It's doubtful that everyone would be honest enough to tell the utility that they installed a bigger breaker knowing about the additional fees. We are responsible for all equipment and wire ahead of the weatherhead for overhead and ahead of the utility section for underground. Our transformer loading calcs are based on customer supplied load info, so any additional load we are unaware of can lead to low voltage complaints by other customers on that transformer, overheating and equipment damage or overloaded service drops. Seen it more than a few times. My personal philosophy is: Hope for the best and plan for the worst.

I guess meter/service guys like me are a little cynical when we see the extent some people are willing to go to to steal power or avoid facility charges. Especially in today's economy. Up here, marijuana grow houses are becoming more and more of a problem. Most steal power so the extra load doesn't show up on their bill. Search warrants for utility records are often used to identify suspected growers. Kinda like cops....don't trust anybody.

I know this is way off the OP subject, but this is just the way I see it, and I helped write the rules.

What about legal services with multiple disconnecting means- say you have six 200 amp mains with only 800 amp supply conductors because the load calculations tell you there is less than 800 amps of connected load? Is your POCO going to supply that with transformer and conductors rated for 1200 amps or are you going to figure the 800 amps worst case? I'm willing to bet most POCO around here will not even have a transformer rated for 800 amps in most cases, unless there is a fairly continuous load at or near that 800 amp level.

Had a couple school buildings a few years back fed from one POCO service. Between the two buildings we had service disconnects of 400, 200, 200, and 200 amps - 1000 amps. They only supplied this with 350 copper. I don't recall NEC calculations -and they would have been fairly rough calculations at that but maybe would have resulted in a single disconnect of only 600 amps, yet POCO demand data on that same service last year when we did some major upgrading was only in the 200-300 range.

More often then not 200 amp panels have many more breaker spaces available than a 100 amp panel. If I bought a main lug 200 amp panel just for the extra breaker spaces and then installed a backfed 100 amp breaker as the main, it's ridiculous to think you'd deny service just because the panel has a 200 amp bus rating.

If you have a panel with a 150 amp main breaker chances are the bus is the same bus that is in a 200 or even a 225 amp panel. Same goes for 100 and 125 amp panels, the bus is generally the same thing in either panel. Then when you step up to the 250 to 400 amp series - the bus is a 400 amp bus, you just happen to select a 250, 300 or 350 amp breaker if that is what you desire, and you will not save all that much changing it later as the main is not cheap, and probably will not have much demand for the one you take out either.

I find this debate quite interesting since most residential services are grossly oversized using NEC calculations compared to what they draw in the real world. Power company logs of actual usage prove this.

:thumbsup::thumbsup::thumbsup:
Other than when there is electric heat involved, I can't remember ever clamping on to the main feed to a dwelling and measuring much more than 60 amps or so even if the main feed had 400 amps of overcurrent protection. I'm sure there could be a few instances where it could raise more than that in some cases but those are going to be short in duration and probably not much of a problem.

 

[meternerd]

Well, OK. Since we started down this road..... If a multi-meter service is installed, the contractor requests whatever size service he needs and that's what the fees are based on. We usually size the transformer and conductors (overhead will be smaller wire because it's open air instead of in conduit) based on 80% of that figure (max continuous load per NEC). Each individual meter is protected from damage by its individual main breaker. From an economic standpoint, it's cheaper to install a larger transformer in the beginning than to have to go back and upsize later due to complaints about low voltage, flickering lights or a blown primary fuse due to overload. On the other hand, if a single meter service has a 200A panel, we assume 80% of 200A even if the main is 100A. If I go to a new installation that has a 400A meter panel, but the customer says it's a 200A service, we have a problem, regardless of breaker size. 400A sockets get a Class 320 meter. Some 400A panels have provision for two 200A breakers, but the service will still be sized as 400A, even if only one breaker is installed.

In reality, 100A services are pretty rare, so all standard residential services get a 200A meter even if they are rated 100A. I can't even remember the last time I inspected a new 100A service. We are soon changing our rates to 200A or less rather than 100A and 200A. That will eliminate a lot of paperwork and probably the incentive to "manipulate" the system.

I know this all sounds pretty convoluted, but we are trying to foresee potential problems before they bite us in the ... Power companies usually have a bad enough reputation anyway, so if we can keep our service cheaper and more reliable, that's what we'll try to do.

 

[kwired]

Well, OK. Since we started down this road..... If a multi-meter service is installed, the contractor requests whatever size service he needs and that's what the fees are based on. We usually size the transformer and conductors (overhead will be smaller wire because it's open air instead of in conduit) based on 80% of that figure (max continuous load per NEC). Each individual meter is protected from damage by its individual main breaker. From an economic standpoint, it's cheaper to install a larger transformer in the beginning than to have to go back and upsize later due to complaints about low voltage, flickering lights or a blown primary fuse due to overload. On the other hand, if a single meter service has a 200A panel, we assume 80% of 200A even if the main is 100A. If I go to a new installation that has a 400A meter panel, but the customer says it's a 200A service, we have a problem, regardless of breaker size. 400A sockets get a Class 320 meter. Some 400A panels have provision for two 200A breakers, but the service will still be sized as 400A, even if only one breaker is installed.

In reality, 100A services are pretty rare, so all standard residential services get a 200A meter even if they are rated 100A. I can't even remember the last time I inspected a new 100A service. We are soon changing our rates to 200A or less rather than 100A and 200A. That will eliminate a lot of paperwork and probably the incentive to "manipulate" the system.

I know this all sounds pretty convoluted, but we are trying to foresee potential problems before they bite us in the ... Power companies usually have a bad enough reputation anyway, so if we can keep our service cheaper and more reliable, that's what we'll try to do.

How about multiple service disconnecting means, but service conductors sized for total calculated load - no multi metering? Example of something I installed recently - 800 amp main lug I-line panel, with no more than 6 breakers installed as service disconnecting means. This one had 2 - 400 amp breakers, and 2-125 amp breakers. Calculated load was about 600 amps, worst case, past demand was well below that but there will be future chiller installed, but current AC load will also disappear when the chiller is installed. I ran three parallel sets of 350 aluminum service conductors giving an ampacity of 750 amps. Metering is CT's and is done at the transformer location. What size of service is this to your utility?

The serving utility put this on a 150 kVA transformer that happened to be kind of existing - and was serving another building owned by same customer it is due for replacement in next few years anyway so there was no charge for this transformer, but will likely increase to a 225 when the chiller is installed in a couple years or so. If they install the 225 now without the load to justify it, it will cost a lot more than if they install it when there is load to justify it. Their transformer charge is not based solely on the cost of the transformer, but somehow factors in the expected load and return on investment as well. The other building that had the old 150 kVA transformer had a replacement installed that was due for replacement anyway, it was around 40 years old. I bet many utility companies would not make that kind of deal with a customer though, and sock them hard with upgrade charges.

 

[meternerd]

How about multiple service disconnecting means, but service conductors sized for total calculated load - no multi metering? Example of something I installed recently - 800 amp main lug I-line panel, with no more than 6 breakers installed as service disconnecting means. This one had 2 - 400 amp breakers, and 2-125 amp breakers. Calculated load was about 600 amps, worst case, past demand was well below that but there will be future chiller installed, but current AC load will also disappear when the chiller is installed. I ran three parallel sets of 350 aluminum service conductors giving an ampacity of 750 amps. Metering is CT's and is done at the transformer location. What size of service is this to your utility?

The serving utility put this on a 150 kVA transformer that happened to be kind of existing - and was serving another building owned by same customer it is due for replacement in next few years anyway so there was no charge for this transformer, but will likely increase to a 225 when the chiller is installed in a couple years or so. If they install the 225 now without the load to justify it, it will cost a lot more than if they install it when there is load to justify it. Their transformer charge is not based solely on the cost of the transformer, but somehow factors in the expected load and return on investment as well. The other building that had the old 150 kVA transformer had a replacement installed that was due for replacement anyway, it was around 40 years old. I bet many utility companies would not make that kind of deal with a customer though, and sock them hard with upgrade charges.

Probably 800A, but if it's a single commercial customer, we'd consider expected load as well. You didn't say voltage or phases, but if other customers may later be fed off of the same transformer (such as 120/208 network services), we'd consider that as well when sizing equipment. Any non-residential service over 200A gets CT's, so that would mean a demand meter, which would give us peak demand info. We normally don't meter at the transformer because we go by EUSERC, which specifies switchgear metering. Also, multiple customers require multiple meters. Larger commercial metering is is considered on a case by case basis. As I said before, with standard 120/240 single phase residential, it's a pretty hard and fast rule. Other services are more up to the engineering department. As far as cost, the differences in transformer costs versus labor, wiring, metering etc. is usually not significant. We figure it's better to oversize than undersize. Loads usually tend to increase over time rather than decrease with most commercial or industrial services.

 

[kwired]

Probably 800A, but if it's a single commercial customer, we'd consider expected load as well. You didn't say voltage or phases, but if other customers may later be fed off of the same transformer (such as 120/208 network services), we'd consider that as well when sizing equipment. Any non-residential service over 200A gets CT's, so that would mean a demand meter, which would give us peak demand info. We normally don't meter at the transformer because we go by EUSERC, which specifies switchgear metering. Also, multiple customers require multiple meters. Larger commercial metering is is considered on a case by case basis. As I said before, with standard 120/240 single phase residential, it's a pretty hard and fast rule. Other services are more up to the engineering department. As far as cost, the differences in transformer costs versus labor, wiring, metering etc. is usually not significant. We figure it's better to oversize than undersize. Loads usually tend to increase over time rather than decrease with most commercial or industrial services.

Why does it matter if it is a single customer on the transformer or not? Voltage and number of phases kind of doesn't matter for the specific question of how many amps is the service. All that matters is how much expected load there is at whatever voltage and number of phases we have.

This instance was a school with multiple buildings 208/120 three phase was the supply, we revamped the service to two of the buildings that had been single phase in the past, new HVAC equipment was installed with three phase circulation pumps, no real significant load change in KVA but the change to three phase and an increase in capacity was in anticipation of a second phase of HVAC upgrades in a couple years which will include a chiller, that is the reasoning for the deal with not installing the larger transformer up front, but they happened to have a transformer that needed replaced for regular maintenance purposes that served a third building owned by same school as well that the POCO was nice enough to let them use as a temporary supply until they get the chiller and then they will have the load to justify the larger transformer and can install it at a lesser cost.

That said I have another school I do work at. It has a 2000 amp switchboard with 2000 amp main installed. It is 120/240 single phase supply. I have never needed to remove covers on the main switchboard so I am not certain what the supply conductors are. But the transformer outside is a pad mount 100 kVA - far from 2000 amps of capability on that one.

 

[meternerd]

OK....I'm done. Way off the OP post, and we could spend all day talking about specific situations. I'll answer your one question about one customer. We size transformers by number of services that are shared. Each service is considered 80% of panel rating. Additional customers on the same transformer add up to total possible load on the transformer. If it gets too close to transformer rating, we put on a recorder and check loads. If actual load is close to max, we set another transformer and split the loads. I can't speak for other utilities, but this seems to work for us, so we won't likely change. Here in the Tahoe resort mountain area, we have MANY second homeowners, so if a transformer is fine most of the time, ski season or 4th of July is a whole different story. Everybody comes up, turns on the heat and fires up the hot tub. System load almost doubles! We do the best we can.

This has been a fun exercise but I'm retired now, so I'm trying to forget all this stuff so I can sleep at night.

I really like this forum, because as a utility guy, Code is probably my weakest point. Most of the time, we're exempt. But we are also the water utility, so all of our pump stations have to be up to code. Thank God, the other tech is a major code guy, so I lean (oops...leaned, now that I'm retired) on him a lot.

Thanks for all your input. I'll probably check back once in a while, but trying to remember all of the reasons we did the things we did is giving me a headache.

Thanks for all of your input . I've learned a lot, and just because that's the way WE do things doesn't mean every other utility does it the same way. Just cut 'em some slack. The field guys are NOT the ones who set poilcy, they're just the ones who have to try and explain it to the customer.

Good night.