Connecting to a Switchboard

[Ctay005]

I'm currently doing a design for a small commercial system (25kW) in CA and the service is a Siemens switchboard with 6 meters. Each feeding different suites in the building. I'm trying to find out the interconnection method but I don't think I was given enough photos to make that call. So I'm wondering, 1) where is the best place (typically, I know things differ) to connect to a switchboard like this. 2) What additional pictures will I need?

I've done a few commercial designs but I haven't done with a panel like this before with all of the different meters and I didnt get photos of any of the supply side of things.

I've attached the few photos that I have. (Attaching didnt work too well.... Edit: Fixed )

 

[Carultch]

I'm currently doing a design for a small commercial system (25kW) in CA and the service is a Siemens switchboard with 6 meters. Each feeding different suites in the building. I'm trying to find out the interconnection method but I don't think I was given enough photos to make that call. So I'm wondering, 1) where is the best place (typically, I know things differ) to connect to a switchboard like this. 2) What additional pictures will I need?

I've done a few commercial designs but I haven't done with a panel like this before with all of the different meters and I didnt get photos of any of the supply side of things.

I've attached the few photos that I have. (Attaching didnt work too well.... Edit: Fixed )

I recommend connecting opposite the main supply, and following the "120% rule", like you do for panelboards. So get the busbar rating, the main supply rating, and whether there is a position available opposite the main supply.

Be aware that switchboards might contain a horizontal bus and a vertical bus, each with different ampacities. Like a 2000A main horizontal bus, and 600A branch vertical busses. If you are using a vertical bus to do this, get an inventory of existing breakers on it, so that you can use the rule for "sum of breakers excluding main supply, shall not exceed busbar ampacity".

 

[jaggedben]

The first question you have answer is which meter(s) you are trying to backfeed, or if you are going to put in a new meter. That's something that should have been figured out by sales so I feel for you if it was not.

One option would be to split the system into multiple systems and interconnect them at whatever panels those breakers are feeding, assuming you can appropriately match system size to each meter's electrical usage. Follow the 120% rule, etc, for the subpanels (and feeders if AHJ requires). I don't see a breaker bigger than 200A so you probably have to split 25kW into at least two systems for this to work.

Another option might be to install a new meter in the switchboard, and apply for a Virtual Net Metering account. The solar is then the only thing on that meter and the utility's billing software apportions the credits to the other meters according to how the client chooses. You'd have to find out from the manufacturer if it's possible to install a new meter, and there will be some fees and costs from the utility for the new meter.

 

[jaggedben]

Another thought: You may be able to do supply side connections to busbars in between the meters and breakers, if you can't meet the 120% rule or have other problems interconnecting to subpanels. You still need to find out what meter(s) should be backfed: probably this option is most worth pursuing if it's only one meter. So photos of those busbars would be useful for seeing if that is feasible. To know whether your AHJ will approve such a connection you'd need to have a conversation with them. You may be required to either get a letter from Seimens that your method is okay, or pay UL to come out and field list your installation.

 

[Ctay005]

Another thought: You may be able to do supply side connections to busbars in between the meters and breakers, if you can't meet the 120% rule or have other problems interconnecting to subpanels. You still need to find out what meter(s) should be backfed: probably this option is most worth pursuing if it's only one meter. So photos of those busbars would be useful for seeing if that is feasible. To know whether your AHJ will approve such a connection you'd need to have a conversation with them. You may be required to either get a letter from Seimens that your method is okay, or pay UL to come out and field list your installation.

If I go the virtual NEM route, does the new meter need to be installed with the others or can it be installed as a seperate unit? Theres no space in the switchboard so that is definitely an option and it is what PG&E said would be a possible solution. If thats the case a supply side connection before the other 6 meters would be neccesary correct? That way the power doesnt backfeed through anything but the new virtual meter?

 

[ggunn]

If I go the virtual NEM route, does the new meter need to be installed with the others or can it be installed as a seperate unit? Theres no space in the switchboard so that is definitely an option and it is what PG&E said would be a possible solution. If thats the case a supply side connection before the other 6 meters would be neccesary correct? That way the power doesnt backfeed through anything but the new virtual meter?

Yes, if you can get approval from the AHJ to do virtual net metering, the solar feed needs to be between the service and the point where it splits to the other meters.

 

[shortcircuit2]

I'm currently doing a design for a small commercial system (25kW) in CA and the service is a Siemens switchboard with 6 meters. Each feeding different suites in the building. I'm trying to find out the interconnection method but I don't think I was given enough photos to make that call. So I'm wondering, 1) where is the best place (typically, I know things differ) to connect to a switchboard like this. 2) What additional pictures will I need?

I've done a few commercial designs but I haven't done with a panel like this before with all of the different meters and I didnt get photos of any of the supply side of things.

I've attached the few photos that I have. (Attaching didnt work too well.... Edit: Fixed )

Tap the 200-amp feeder (#5) for the house panel and put a main in the house panel for protection of that panel. NET metering can be through the house panel meter. Do your RGM anyway you want from there...

 

[jaggedben]

Tap the 200-amp feeder (#5) for the house panel and put a main in the house panel for protection of that panel. NET metering can be through the house panel meter. Do your RGM anyway you want from there...

For regulatory reasons, that won't work in California, unless that meter will have net annual usage above zero. (The meters may be on different rates, too. As I stated above, whoever sold this should have known which meter(s) were supposed to be backfed. The economic objective may trump technical considerations.)

Also, while the load side tap is potentially a good idea, he may have to wait until January to invoke the 2016 CEC which will have the 2014 NEC rules. Sucks if they want to get the federal tax credit this year.

 

[Engineer#4827502]

If I go the virtual NEM route, does the new meter need to be installed with the others or can it be installed as a seperate unit? Theres no space in the switchboard so that is definitely an option and it is what PG&E said would be a possible solution. If thats the case a supply side connection before the other 6 meters would be neccesary correct? That way the power doesnt backfeed through anything but the new virtual meter?

Virtual net metering is essentially installing a new 'solar service' that can credit the meters. There is also Net Metering Aggregation which is slightly different. That allows backfeeding one meter to credit other meters. I believe for that to apply, the other services need to be on the same account.

 

[ggunn]

Virtual net metering is essentially installing a new 'solar service' that can credit the meters. There is also Net Metering Aggregation which is slightly different. That allows backfeeding one meter to credit other meters. I believe for that to apply, the other services need to be on the same account.

It all depends on what the AHJ will allow. The math is pretty straightforward but the AHJ has to agree to do it.

 

[jaggedben]

Virtual net metering is essentially installing a new 'solar service' that can credit the meters. There is also Net Metering Aggregation which is slightly different. That allows backfeeding one meter to credit other meters. I believe for that to apply, the other services need to be on the same account.

It might seem like a fine point, but for PG&E it must be a new meter on the same service. There can only be one service point. You cannot install a new service or use a meter connected to a different service to credit the meter you want, even if the meters are on the same account. (Put another way, PG&E does not allow 'community solar'.) The meters credited can be on multiple accounts with the production credits divided according to pre-arranged percentages, but they must all be connected to the same service.

Other utilities and AHJs may vary, but the OP did mention PG&E in this case.

 

[Ctay005]

It might seem like a fine point, but for PG&E it must be a new meter on the same service. There can only be one service point. You cannot install a new service or use a meter connected to a different service to credit the meter you want, even if the meters are on the same account. (Put another way, PG&E does not allow 'community solar'.) The meters credited can be on multiple accounts with the production credits divided according to pre-arranged percentages, but they must all be connected to the same service.

Other utilities and AHJs may vary, but the OP did mention PG&E in this case.

Yeah we will be dealing with PG&E so their rules apply here and they tend to be difficult to get a hold of sometimes but I'll give them a call and see what we can do. As far as interconnection goes, I'm going to get some more photos of the service and of the busbars. Siemens told me that a recert of the UL listing will be required unless there are already designated holes on the busbars intended for taps to be installed.

So pretty much until I get the new photos of the guts of the panel I'm kind of at a standstill. The building is one big barn style building with multiple shops so I'm sure they're on different rate schedules depending on their usage so the whole community solar thing probably wont work but I'll see if PG&E has any other suggestions since I'm sure this isnt the first time they've dealt with this sort of situation on a commercial building.

 

[ggunn]

Yeah we will be dealing with PG&E so their rules apply here and they tend to be difficult to get a hold of sometimes but I'll give them a call and see what we can do. As far as interconnection goes, I'm going to get some more photos of the service and of the busbars. Siemens told me that a recert of the UL listing will be required unless there are already designated holes on the busbars intended for taps to be installed.

So pretty much until I get the new photos of the guts of the panel I'm kind of at a standstill. The building is one big barn style building with multiple shops so I'm sure they're on different rate schedules depending on their usage so the whole community solar thing probably wont work but I'll see if PG&E has any other suggestions since I'm sure this isnt the first time they've dealt with this sort of situation on a commercial building.

Sometimes in addition to tenants' meters there is another meter for common areas, and depending on mainly the AC and lighting, the usage logged by that meter can be substantial. Backfeeding a meter like that can sometimes work.

 

[electrofelon]

As far as interconnection goes, I'm going to get some more photos of the service and of the busbars. Siemens told me that a recert of the UL listing will be required unless there are already designated holes on the busbars intended for taps to be installed.

You man to "forget" you heard that though and see what your AHJ says. They may be more lax. For example, I have had inspectors tell me that I may change lugs or add lugs as long as there are listed and on existing holes. Bus bar conmections/splice points seem to always be nema standard patterns so lugs will typically fit there as an option....

 

[pv_n00b]

You man to "forget" you heard that though and see what your AHJ says. They may be more lax. For example, I have had inspectors tell me that I may change lugs or add lugs as long as there are listed and on existing holes. Bus bar conmections/splice points seem to always be nema standard patterns so lugs will typically fit there as an option....

I would caution you not to forget what the manufacturer told you, it's an important point to keep in mind. No manufacturer is going to approve doing something in their UL listed equipment that it was not designed to do. And the chances we will run across equipment that was designed for a supply side PV system interconnection is currently close to zero.

So we should be cognizant of the fact that we are making stuff up as we go when we attach lugs to any place that is convenient to use in a panel or switchboard. If we drill a bus bar and attach a lug, if we use an existing hole to attach a lug that was not identified for that purpose, if we use an existing bolt or stud to attach a lug that was not identified for that purpose we are not following any installation instructions, we have no legal protection if something goes wrong, and we may very well be creating a hazardous situation. Having the AHJ approve it does not protect us, it just makes the AHJ a co-defendent. The only way to be protected is to have the equipment field inspected by a NRTL and relisted. Then you can say it is UL approved and listed. Unfortunately this is expensive and most people feel the exposure is so small it's worth the risk to keep the cost down.

True, the odds of something bad happening are low, but we should all be aware that we are swinging in the wind based on the way I see a lot of these supply side interconnections being done.

 

[electrofelon]

I would caution you not to forget what the manufacturer told you, it's an important point to keep in mind. No manufacturer is going to approve doing something in their UL listed equipment that it was not designed to do. And the chances we will run across equipment that was designed for a supply side PV system interconnection is currently close to zero.

So we should be cognizant of the fact that we are making stuff up as we go when we attach lugs to any place that is convenient to use in a panel or switchboard. If we drill a bus bar and attach a lug, if we use an existing hole to attach a lug that was not identified for that purpose, if we use an existing bolt or stud to attach a lug that was not identified for that purpose we are not following any installation instructions, we have no legal protection if something goes wrong, and we may very well be creating a hazardous situation. Having the AHJ approve it does not protect us, it just makes the AHJ a co-defendent. The only way to be protected is to have the equipment field inspected by a NRTL and relisted. Then you can say it is UL approved and listed. Unfortunately this is expensive and most people feel the exposure is so small it's worth the risk to keep the cost down.

True, the odds of something bad happening are low, but we should all be aware that we are swinging in the wind based on the way I see a lot of these supply side interconnections being done.

We have debated this before, and I guess we will just have to "agree to disagree" about whether or not is acceptable to bolt and/or change lugs on busbars.

 

[pv_n00b]

I have a problem when someone says, forget what the manufacturer says about their own equipment. Feel free to do your own thing, but do it knowing all the facts, including what the manufacturer's position is on the subject, and UL's position, the NEC's position, the AHJ's position, and your own position. To do otherwise is just willful ignorance of the subject. "I'm going to forget I heard something because knowing it makes my job harder", is not a recipe for a long life in the electrical business.

 

[ggunn]

I would caution you not to forget what the manufacturer told you, it's an important point to keep in mind. No manufacturer is going to approve doing something in their UL listed equipment that it was not designed to do. And the chances we will run across equipment that was designed for a supply side PV system interconnection is currently close to zero.

So we should be cognizant of the fact that we are making stuff up as we go when we attach lugs to any place that is convenient to use in a panel or switchboard. If we drill a bus bar and attach a lug, if we use an existing hole to attach a lug that was not identified for that purpose, if we use an existing bolt or stud to attach a lug that was not identified for that purpose we are not following any installation instructions, we have no legal protection if something goes wrong, and we may very well be creating a hazardous situation. Having the AHJ approve it does not protect us, it just makes the AHJ a co-defendent. The only way to be protected is to have the equipment field inspected by a NRTL and relisted. Then you can say it is UL approved and listed. Unfortunately this is expensive and most people feel the exposure is so small it's worth the risk to keep the cost down.

True, the odds of something bad happening are low, but we should all be aware that we are swinging in the wind based on the way I see a lot of these supply side interconnections being done.

I ran into this situation twice, where I wanted to mount a supply side connection on vacant perforations on the busbars of the main breaker of a large MDP and the AHJ wanted it in writing from the MDP manufacturer that it was OK. In both cases I found it very hard to get it, but it wasn't because it wasn't OK, it was because they were wondering why I was asking. When I finally got to the correct person in each manufacturer's tech support, they told me that of course I could do it.