Bonding of Permanent Generator

[mwh1023]

I have a new generator installation, 150 kW 208V 3-phase on a concrete pad. The generator will come equipped with (2) 400A breakers to feed (2) electrical panels (with MLO terminals) in the building via (2) 400A Automatic Transfer switches. The ATS's will switch the neutral making this a seperately derived system. My plan is to install (4) 500 kcmil copper conductors between the ATS and the 400 amp breaker for each panel with NO equipment grounding conductors. The 500 kcmil is rated at 380 amps, 75 degree column of 310.15(B). I will install a main bonding jumper in the generator based on the (2) parallel feeds, or 1000 kcmil and use a 2/0 copper conductor based on 250.66. I will also connect a 2/0 copper to building steel and supplement this with a #6 copper to a ground rod. In my opinion the ground rod is not required, but the generator manual states the installation should have one. Finally, here is my question: Does 445.13 apply when you have OCPD's at the generator? Should i install 600 kcmil to carry the full 400 amps? If wondering, the calculated load on each panel is in the low 200's as the generator was sized for future expansion.

Thanks,

Mike

 

[hurk27]

I have a new generator installation, 150 kW 208V 3-phase on a concrete pad. The generator will come equipped with (2) 400A breakers to feed (2) electrical panels (with MLO terminals) in the building via (2) 400A Automatic Transfer switches. The ATS's will switch the neutral making this a seperately derived system. My plan is to install (4) 500 kcmil copper conductors between the ATS and the 400 amp breaker for each panel with NO equipment grounding conductors. The 500 kcmil is rated at 380 amps, 75 degree column of 310.15(B). I will install a main bonding jumper in the generator based on the (2) parallel feeds, or 1000 kcmil and use a 2/0 copper conductor based on 250.66. I will also connect a 2/0 copper to building steel and supplement this with a #6 copper to a ground rod. In my opinion the ground rod is not required, but the generator manual states the installation should have one. Finally, here is my question: Does 445.13 apply when you have OCPD's at the generator? Should i install 600 kcmil to carry the full 400 amps? If wondering, the calculated load on each panel is in the low 200's as the generator was sized for future expansion.

Thanks,

Mike

First what size breaker is on the generator?

Second is you only have 416 amps available from this generator and your feeding two 400 amp panels that you say have a calculated load of over 200 amps, I see no future in this (no pun intended) and you might even be over the 416 amps that would allow you to be able to use a ATS?

Third 445.13 require's that the conductor's have a rating of 115% of the nameplate current rating of the generator, this would not allow the 500's which would require conductors rated at least 478.4 amps capacity.

 

[texie]

I'm with you except for the No EGC from the genset breaker to the ATS. You still need an EGC as the fault return path when load is on genset. Are you using metallic conduit as the EGC?

 

[hurk27]

I'm with you except for the No EGC from the genset breaker to the ATS. You still need an EGC as the fault return path when load is on genset. Are you using metallic conduit as the EGC?

I agree you still have to run an EGC, a generator is not a service and the neutral is not a service conductor and they are feeders.

I should have asked if he is using a 4-pole ATS as if not then you can't bond at the generator because of the bond at the service disconnect or you will parallel the neutral.

Also I want to point out that table 310.15(B)(6) is only for conductors that feed a dwelling and only if they are feeding the whole load, table 310.16 is the correct table and it will require 800 kcmil for the 478.4 amps

 

[mwh1023]

The manufacturer states that the generator equipped with an upgraded alternator is rated at 150 kW/188 kVA and capable of producing 520 amps at 208V 3-phase. I will have the (2) 400 amp breakers in the generatorwhich are probably a bit oversized, but the manufacturer allows the installation. The ATS's will be programmed to have delayed start and the following are the panels and loads. Keep in mind that all actual loads have been given to the generator supplier where their calculation sheets have verified the sizing.

Panel A rated at 400 amps and will have a 225A breaker that feeds a 80 kW UPS system which currently has only an 18 kW draw. The owner wanted me to size this with a future load of up to 64 kW. I will also have a 100 amp breaker that feeds a 100 amp 3-phase panel that will feed around 15 receptacles and 20 2x4 2-lamp light fixtures with 32W lamps.

Panel B (delayed transfer) is rated at 400 amps and will have a 150A breaker that feeds a Canatal Unit that has a FLA of 108 amps at 208V 3-phase. This panel will also have a 100 amp breaker that feeds a 2nd redundant Canatal Unit that has a FLA of 74 amps, (will not run at the same time as the other Canatal Unit.)

 

[texie]

I agree you still have to run an EGC, a generator is not a service and the neutral is not a service conductor and they are feeders.

I should have asked if he is using a 4-pole ATS as if not then you can't bond at the generator because of the bond at the service disconnect or you will parallel the neutral.

Also I want to point out that table 310.15(B)(6) is only for conductors that feed a dwelling and only if they are feeding the whole load, table 310.16 is the correct table and it will require 800 kcmil for the 478.4 amps

The OP stated 4 pole ATS. Who said anything about service conductors? Of course they are feeders.
I don't think the OP was referring to 310.15 (B) (6) but rather using the calculated load argument. I'll admit that is weak.

 

[hurk27]

Wow I have never seen a generator manufacture install two breakers like this, the 188kva is most likely a peak rating which you would still be required to use the 150kva rating to calculate the 115% from, but I have no idea if tap rules would allow any smaller conductors?

Also I do not see how you can get 520 amps out of 150kva, you can't go by a peak rating, if the generator is rated at the 188kva then you have to still add the 15% to your conductors as per 445.13 which your looking at over 600 amps, the 520 amps actually 521 amps is basing the generator as rated 188kva not 150kva?

I don't see how you can get around the 445.13 requirement?

Maybe we can get someone who might be more experienced with a install like this to chime in. there might be a tap rule, I'm just not sure?

 

[texie]

The manufacturer states that the generator equipped with an upgraded alternator is rated at 150 kW/188 kVA and capable of producing 520 amps at 208V 3-phase. I will have the (2) 400 amp breakers in the generatorwhich are probably a bit oversized, but the manufacturer allows the installation. The ATS's will be programmed to have delayed start and the following are the panels and loads. Keep in mind that all actual loads have been given to the generator supplier where their calculation sheets have verified the sizing.

Panel A rated at 400 amps and will have a 225A breaker that feeds a 80 kW UPS system which currently has only an 18 kW draw. The owner wanted me to size this with a future load of up to 64 kW. I will also have a 100 amp breaker that feeds a 100 amp 3-phase panel that will feed around 15 receptacles and 20 2x4 2-lamp light fixtures with 32W lamps.

Panel B (delayed transfer) is rated at 400 amps and will have a 150A breaker that feeds a Canatal Unit that has a FLA of 108 amps at 208V 3-phase. This panel will also have a 100 amp breaker that feeds a 2nd redundant Canatal Unit that has a FLA of 74 amps, (will not run at the same time as the other Canatal Unit.)

150 KW/188 KVA is "standard" not an upgrade. All gensets in this range are this way as they are rated at .8 power factor. Given what you are saying about the load type and quantity I would be real iffy of this install without careful engineering consideration.

 

[texie]

Wow I have never seen a generator manufacture install two breakers like this, the 188kva is most likely a peak rating which you would still be required to use the 150kva rating to calculate the 115% from, but I have no idea if tap rules would allow any smaller conductors?

Also I do not see how you can get 520 amps out of 150kva, you can't go by a peak rating, if the generator is rated at the 188kva then you have to still add the 15% to your conductors as per 445.13 which your looking at over 600 amps, the 520 amps actually 521 amps is basing the generator as rated 188kva not 150kva?

I don't see how you can get around the 445.13 requirement?

Maybe we can get someone who might be more experienced with a install like this to chime in. there might be a tap rule, I'm just not sure?

In the recent years multiple factory breakers have become pretty common as it simplfies things such as seperating a fire pump and other loads.
Generators are different than say, a transformer which is rated in VA. A generator is rated in W (which determins the power required to drive it) and VA (apparent power) which you use for sizing conductors and gear. It would be rare to find a genset of this size (150KW) not rated at 188 KVA (520 A)
445.13 does not apply as these are feeders on the load side of factory breakers.
Note that you can't size conductors, etc from watts. You will end up 20% shy in this case.

 

[mwh1023]

Thanlks for the quick replies. My thoughts are 445.13 applies if there is no breaker in the generator. I believe the 115% sizing would be applied to the factory conductors that feed the line side of the breakers in the generator. Most of the examples I see in grounding texts show a generator WITHOUT any breaker(s) in the genset. The ATS's are 4-pole, so it is seperately derived. I am establishing the main bonding in the generator so I agree I will need EGC's installed from the breaker to the ATS's and Panel's. I will be utilizing PVC conduit from the generator to the building. By the way, I have had an engineer look at the calculation sheet that was emailed to me from the generator supplier and his comments were that "he admits that it looks "tight" but some generator alternators function better than others and sometimes you hit the "sweet spot" with a certain manufacturer and they are able to supply a higher amperage than another manufacturer".

 

[texie]

Hurk27,
It might be helpful consider this:
Generator is rated 150 KW/188 KVA.
It will carry a purely resistive load of 416 amps = 150 KW
It will carry an inductive load at 188 amps @.8 PF =150 KW
If you put a purely resistive load of 188 amps on the genset it will overload the engine.

 

[mwh1023]

Based on the information I gave the manufacturer, the 64 kW future load of the UPS, the (2) Canatal Units running AT THE SAME TIME as it is a possibility that someday the owner may run these together, the receptacles and lights and they have given me a total connected load of 122 kW and 133 kVA, then sized the generator to 150 kW.

 

[mwh1023]

Hurk27,
It might be helpful consider this:
Generator is rated 150 KW/188 KVA.
It will carry a purely resistive load of 416 amps = 150 KW
It will carry an inductive load at 188 amps @.8 PF =150 KW
If you put a purely resistive load of 188 amps on the genset it will overload the engine.

I agree with your thoughts. What I'm having a tough time with is the (2) 400A breakers in the genset. I'm feeding the (2) panels from the MDP with (2) runs of 500 kcmil off of 400A breakers because the ATS's and Panels are RATED at 400A and it gives me a little expansion, but I know that the generator will not produce two loads of 400A? But yet the manufacturer is ok with it?

 

[texie]

Based on the information I gave the manufacturer, the 64 kW future load of the UPS, the (2) Canatal Units running AT THE SAME TIME as it is a possibility that someday the owner may run these together, the receptacles and lights and they have given me a total connected load of 122 kW and 133 kVA, then sized the generator to 150 kW.

As I mentioned previously, I would be real careful here. The load (with the furture stuff) and the kind of load could be an issue. The type of UPS also will have an impact. Some manufacturers, such as Cummins or Kohler are very good (read competent) in helping size units. There are some I would not trust at all. IMO you need an engineer (with experience in this type of application), the UPS maker and the genset maker to collaborate. These kind of genset applications are not to be treated lightly or you could end up with an unacceptable situation.

 

[texie]

Hurk27,
It might be helpful consider this:
Generator is rated 150 KW/188 KVA.
It will carry a purely resistive load of 416 amps = 150 KW
It will carry an inductive load at 188 amps @.8 PF =150 KW
If you put a purely resistive load of 188 amps on the genset it will overload the engine.

I agree with your thoughts. What I'm having a tough time with is the (2) 400A breakers in the genset. I'm feeding the (2) panels from the MDP with (2) runs of 500 kcmil off of 400A breakers because the ATS's and Panels are RATED at 400A and it gives me a little expansion, but I know that the generator will not produce two loads of 400A? But yet the manufacturer is ok with it?

Sorry, major typo... those 188 A numbers should have been 520 A. Not sure if it is a senior moment or just late. Sorry for the confusion.:roll:

 

[hurk27]

Sorry, major typo... those 188 A numbers should have been 520 A. Not sure if it is a senior moment or just late. Sorry for the confusion.:roll:

Ok I just did some googling and I only find Cummins with the rating of the OP'er

Correct 150 kw and 188 kva, not peak like I thought, still you have 520 amps at a pf of .8

Prime ratings are even lower at 135 kw and 169 kva which is where the generator is used off grid or longer run times

445.12 requires the generator to have OCP and I don't see how two 400 amp breakers will meet that as it could be loaded to 800 amps and never trip, although is does have electronic shut down if over loaded so that might count?

just throwing this out so maybe I can learn a little where a generator has multiple breakers as in this case.