generator feeding six meters

[electrofelon]

I have a tricky generator install that I am trying to figure out how to do and thought I would ask for feedback on what I am thinking of doing and also for any other ideas that I have not thought of. This job is for friends so I am trying to keep the costs down for them. The building is a multi use with 4 dwelling units (100 amp feeders), a shop space and a house panel. Service is 400 amp three phase 208, six hot sequenced meters (6 service disconnects, no single main). The shop space is the only three phase panel, rest are 208/120 single phase. They bought a used 3 phase 65 kw generator without discussing it with me so that is what we have to work with. The big question is how to tie this in to the system. My first thought was to get a 400 amp transfer switch and install it after a 400 amp single main but befor the meters. This is likely not feasible for three reasons: 1) cost. its about $4800 for the transfer switch and service disconnect. 2) issue with meters being neutral bonded. I know about the exception for cold sequenced meters, but with a trasfer switch in there not sure if that fits the exception. 3) Utilty probably will not like the meters cold sequences after transfer equipment, not to mention the transfer equip being non metered.

So my thought is to get 5 100 amp DPDT switches and tie them in after the meters. The shop panel may just not get emergency power or we will have to get a three phase switch for that one. So then I could run a single main feeder from the generator and taps off of that to each DPDT switch. Since the generator breaker is greater than 100 amps, I would need an ocpd after the taps but before the switch to protect the switch at its rating. Does that sound feasible or any other ideas? One more thing, they do have a 225 3 phase auto transfer switch that came with the unit but I cant see how that helps us (except maybe using it for the shop) Thanks.

 

[ceb58]

I have a tricky generator install that I am trying to figure out how to do and thought I would ask for feedback on what I am thinking of doing and also for any other ideas that I have not thought of. This job is for friends so I am trying to keep the costs down for them. The building is a multi use with 4 dwelling units (100 amp feeders), a shop space and a house panel. Service is 400 amp three phase 208, six hot sequenced meters (6 service disconnects, no single main). The shop space is the only three phase panel, rest are 208/120 single phase. They bought a used 3 phase 65 kw generator without discussing it with me so that is what we have to work with. The big question is how to tie this in to the system. My first thought was to get a 400 amp transfer switch and install it after a 400 amp single main but befor the meters. This is likely not feasible for three reasons: 1) cost. its about $4800 for the transfer switch and service disconnect. 2) issue with meters being neutral bonded. I know about the exception for cold sequenced meters, but with a trasfer switch in there not sure if that fits the exception. 3) Utilty probably will not like the meters cold sequences after transfer equipment, not to mention the transfer equip being non metered.

So my thought is to get 5 100 amp DPDT switches and tie them in after the meters. The shop panel may just not get emergency power or we will have to get a three phase switch for that one. So then I could run a single main feeder from the generator and taps off of that to each DPDT switch. Since the generator breaker is greater than 100 amps, I would need an ocpd after the taps but before the switch to protect the switch at its rating. Does that sound feasible or any other ideas? One more thing, they do have a 225 3 phase auto transfer switch that came with the unit but I cant see how that helps us (except maybe using it for the shop) Thanks.

You will be better off setting the DPDT switches. If you set an ATS on the service side you must have a disconnect or the ATS must be service rated. You then have to contend with a load calculation for the whole building or do load shedding. With the DPDT switches you already have the disconnects and this would be a manual transfer set up so the load calc. would not come into play.

 

[goldstar]

This job is for friends so I am trying to keep the costs down for them.

There's your first problem.

So my thought is to get 5 100 amp DPDT switches and tie them in after the meters.

They do make 100 amp manual transfer switches. If you use a 3-pole transfer switch make sure you don't transfer the neutral.

One more thing, they do have a 225 3 phase auto transfer switch that came with the unit but I cant see how that helps us (except maybe using it for the shop)

Throw it out. I agree with CEB. Once you use the word automatic you're in a different category. You'll have to use a service rated disconnect and either use a load shedding system or provide the inspector with a connected load summary.

 

[hillbilly1]

You will not be able to use DPDT switches because you will have to switch the neutral since you have only one generator. All of the neutrals would be tied together at the generator regardless if you let the neutral "float" or not. If you use the automatic switch, the load calc would only be required for that service since the rest are manually operated and can be added or shed as necessacary. Put all of the switches past the service disconnect so you will not need service rated switches, you will have to use four and five pole switches anyway.

 

[iwire]

My first thought was to get a 400 amp transfer switch and install it after a 400 amp single main but before the meters.

I think you should put that thought right out of your mind. Along with what you mentioned, your friend and his tenants would be paying the utility company for the use of the generator.

So my thought is to get 5 100 amp DPDT switches and tie them in after the meters.

Much better, these would have to be service rated switches. They would become the service disconnects for each tenant. This results in more issues, the overcurrent protection has to be with the service dicaonect or 'immediately adjacent too', the GEC would have to move back to it and the neutrals and EGC will have to be isolated at what will become sub panels.

Since the generator breaker is greater than 100 amps, I would need an ocpd after the taps but before the switch to protect the switch at its rating.

I need to think on that one, consider we often supply switches at currents above their ratings.

One more thing, they do have a 225 3 phase auto transfer switch that came with the unit but I cant see how that helps us (except maybe using it for the shop)

I would save it for the shop.

Are you planing on using all three phases to supply the 5 single phase panels?

 

[iwire]

You will not be able to use DPDT switches because you will have to switch the neutral since you have only one generator. All of the neutrals would be tied together at the generator regardless if you let the neutral "float" or not.

I may be missing it but I cannot see a problem with 2 pole switches for this as long as neutral is floated at the gen set.

 

[hillbilly1]

I may be missing it but I cannot see a problem with 2 pole switches for this as long as neutral is floated at the gen set.

Even with the neutral floating all of the panel neutrals will physically tied together at the generator, effectively creating a parallel path regardless if the load is on generator or not, if the op had separate generators for each switch, and the neutral was floated, this would not be a problem.

 

[hillbilly1]

You will not be able to use DPDT switches because you will have to switch the neutral since you have only one generator. All of the neutrals would be tied together at the generator regardless if you let the neutral "float" or not. If you use the automatic switch, the load calc would only be required for that service since the rest are manually operated and can be added or shed as necessacary. Put all of the switches past the service disconnect so you will not need service rated switches, you will have to use four and five pole switches anyway.

I meant to say three and four pole switches instead of four and five, also I missed the cold sequence metering, so they would have to be service rated.

 

[electrofelon]

Thanks for the replies and sorry for the delay in responding.

hillbilly1, I am not following your concern with having it set up as a non SDS. Can you elaborate on you concern with a code reference? Thanks.

Whomever, That is interesting about a generator controlled with a manual transfer not being subject to load calcs. What is the code section that states automatics transfer equip needs a load calc and possible shedding but manual does not?

Iwire, The mains are build in to the metering equipment so I would probably but the switches on the load side of the service breaker so I would not have to deal with service rated equipment. I am familiar with the strategy of using a DPDT switch as you service disconnect, but then as you say you still need the OCPD close by. If the switches are service rated I guess it is kind of a toss up which side of the breaker to connect them to? I cant see you one can supply a 100 amp swith with a feeder capable of more than 100 amps - or am I only required to keep the load to 100 or less? REgarding the phasing of the meters, I have not looked in there but I assume they staggered across the three.

Thanks

 

[jrannis]

GDP and 4 pole DTs

GDP and 4 pole DTs

Think of using 3 phase 400 amp panelboard a "generator distribution panel" this would help you with the heartburn that you are having with tapping the disconnects off of a gutter. Plus, simple 100amp double throw switches are an inexpensive item.
I am still a bit foggy about Hillbilly's post concerning a requirement to open the neutrals. I really cant recall the last time I installed a 4 pole ATS

 

[ceb58]

Thanks for the replies and sorry for the delay in responding.

hillbilly1, I am not following your concern with having it set up as a non SDS. Can you elaborate on you concern with a code reference? Thanks.




Whomever, That is interesting about a generator controlled with a manual transfer not being subject to load calcs. What is the code section that states automatics transfer equip needs a load calc and possible shedding but manual does not?

Iwire, The mains are build in to the metering equipment so I would probably but the switches on the load side of the service breaker so I would not have to deal with service rated equipment. I am familiar with the strategy of using a DPDT switch as you service disconnect, but then as you say you still need the OCPD close by. If the switches are service rated I guess it is kind of a toss up which side of the breaker to connect them to? I cant see you one can supply a 100 amp swith with a feeder capable of more than 100 amps - or am I only required to keep the load to 100 or less? REgarding the phasing of the meters, I have not looked in there but I assume they staggered across the three.

Thanks

702.4 Capacity and Rating.

(1) Manual Transfer Equipment.​

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Where manual transferequipment is used, an optional standby system shall haveadequate capacity and rating for the supply of all equipmentintended to be operated at one time. The user of theoptional standby system shall be permitted to select the​

load connected to the system.

(2) Automatic Transfer Equipment.​

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Where automatictransfer equipment is used, an optional standby systemshall comply with (2)(a) or (2)(b).(a) Full Load. The standby source shall be capable ofsupplying the full load that is transferred by the automatictransfer equipment.(b) Load Management. Where a system is employed thatwill automatically manage the connected load, the standbysource shall have a capacity sufficient to supply the maximum​

load that will be connected by the load management system.

Even with the neutral floating all of the panel neutrals will physically tied together at the generator, effectively creating a parallel path regardless if the load is on generator or not, if the op had separate generators for each switch, and the neutral was floated, this would not be a problem.

How is this any different than if it were a single panel?

 

[hillbilly1]

Lets see if this drawing goes thru, I had to crop it a good bit to make it a small enough file. The red arrows shows the paralell neutral paths when used with multiple services and transferswitches.

 

[electrofelon]

Hillbilly,

Ok fair enough but is that a code issue? Where is it stated that a parallel path on a neutral is prohibited? Perhaps the section (cant look it up right now so will paraphrasing) that states "all conductors of a circuit including EGC's must be in the same cable or raceway"?

 

[shortcircuit2]

300.5(I) = Conductors of the same circuit...

 

[shortcircuit2]

I can't open Hillbilly's photo???

 

[shortcircuit2]

How about 250.6 objectionable current?

 

[iwire]

How about 250.6 objectionable current?

How about it?

I can show the same currents on any multiple service disconnect installation without the generator.

 

[shortcircuit2]

OK...your right...same thing. I'm digging thru this thread because I'm trying to figure out if I can supply two seperate buildings on the same property with seperate services with 1 optional standby generator without violating grounding codes. You see...the generator will be connected to 2 grounding electrode systems?

 

[shortcircuit2]

So...say if the neutral fails at building 1.... the neutral current would seek a path thru building 2 back to the utility transfomer at the street...so I'm digging to see if this is acceptable practice.