Transfer switch 3-pole

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slect

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In Mike's Grounding versus Bonding manual on page 37 it shows the proper way to ground and bond a generator and prime power feeding either a 3 or 4 pole transfer switch.
What is the proper way to ground and bond 2-generators with a 3-pole transfer switch ?
 
slect said:
What is the proper way to ground and bond 2-generators with a 3-pole transfer switch ?
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Slect, you need to provide more information. Are two gen sets feeding a transfer switch without a utility source or are two gen sets in parallel feeding a transfer switch with a utility source available. If two gensets are in parallel feeding a solid neutral switch, then you wire per 250.35(B) 1 or 2. If you have 2 gen sets, source 1 and source 2, then you need to provide a switch neutral transfer switch and make each gen set a seperately derived system and wire per 250.30.

Rick
 
Updated generator issue...

Updated generator issue...

Actually it shows a 2 and 3 pole for a single phase system. In the 2 pole the neutral is not switched. The generator is not seperately derived. Bond and ground at the service only. The generator is not bonded. Most residential generators are installed this way. Aart 250.20(d) fpn1
In the 3-pole the neutral is switched. The generator is a seperately derived system. The generator is then bonded and grounded. 250.20(d)
The issue is when you have no prime power. But have 2 generators with a 3-pole transfer switch. One is a backup. Bond and ground just one ? Bond neither but bond at MDP after transfer ?
 
With 2 gen sets, source 1 and source 2, install the bonding jumper at each generator and use a switched neutral transfer switch.

Rick
 
Gen switch

Gen switch

There have been over a hundred looks at this and only 2 responses. Thanks for your effort. Its not a simple fix..
This is an existing system. Looking for a fix that does not include replacing the transfer switch from 3 to 4... (3-phase system)What do you think about not bonding either generator and installing a bonding jumper at the first MDP. There would be no parallel paths as the gen sets would not be bonded. Any fault in either generator or transfer switch would get back to source.. comments ?
 
slect said:
)What do you think about not bonding either generator and installing a bonding jumper at the first MDP. There would be no parallel paths as the gen sets would not be bonded. Any fault in either generator or transfer switch would get back to source.. comments ?
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Select, you will have a violation of article 250.30(A)1 if you install the jumper in the MDP. The system bonding jumper from the SDS to the first OCPD shall be unspliced.

Rick
 
Ok I agree.. How about removing equipment grounding conductors to avoid parallel paths and bond both generators and the MDP.. creating a 4 wire system to the MDP.. 250.30(1) EX. No. 2... says its ok to bond both. But now begs the question do you bond 1 gen set or both ? Again, thanks for your input....
 
Slect, 2 questions have to be answered. Do you have OCP at each generator and are the generator feeders in metal raceway between the gen set and the transfer switch? If no to any of the 2, then it cannot be done.

Rick
 
Slect, one thing you could do if you have a main at the gen set is install the bonding jumper at each unit, eliminate the neutral conductor and make the system a 3-phase 3-wire. Then for all your circuits needing a neutral, install a 3-wire to 4-wire transformer before or after the MDP. Rick
 
Ok, Bond both gen sets as seperately derived systems. Run 3-wire (phase conductors) to 3-pole transfer switch. No Equipment Grounding conductor to Transfer Switch.
Install 3-wire to Transformer with an EGC. Bond as a seperately derived system.
Install 4 wire with an EGC from transformer to MDP. No System Bond at MDP.
Note:
Can not install an ECG from gen to transfer switch as it will create a path back.(neutral) The ECG from transformer will ground the transfer switch.

I will now price up this scenario and the compare the cost to replaing the 3-pole transfer switch with a 4-pole.
Thanks for your help !
Comments ?
 
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Transfer switch 3 pole &4 pole

Transfer switch 3 pole &4 pole

Well in a 3 pole 3 phase transfer switch we use a bond jumper from neutral to ground in the MDP. In a 4 pole transfer switch switched neutral 3 phase we use the the generator neutral to ground bond jumper as the neutral is switched and can be disconnected during transfer . Solid Neutral = MDP Switched Neutral= Genset . We also install a ground rod in each genset . Did not mean to offend anyone just help out with this issue .best to ya
 
Ohmhead, no offense taken. You did not give enough information regarding the gen sets. One or both grounded and bonded ? See some of Rick's previous comments. I just had an inspector tell me its ok in this scenario to bond only 1 gen set. Not sure i agree. I understand not bonding the generator when the other feed to transfer switch is prime power as the neutrals are connected. But 2 gen sets ? Comments ?
 
Well if you have a solid neutral in your transfer switch you can bond in the mdp , if you have a switched neutral you can bond in the generator yes i agree with the inspector but not totally .Ithink he is saying 2 pole is good in mdp but 3 pole is not ?
 
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ohmhead said:
Well if you have a solid neutral in your transfer switch you can bond in the mdp
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ohmhead, If the transfer switch is in between the SDS and the main distribution panel you have to bond in the SDS.(250.30(A)1). If the transfer switch was not in between i would agree.
 
slect said:
I just had an inspector tell me its ok in this scenario to bond only 1 gen set. Not sure i agree. I understand not bonding the generator when the other feed to transfer switch is prime power as the neutrals are connected. But 2 gen sets ? Comments ?
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Slect, you have the choice of bonding either at the SDS or the first OCPD. If there is equipment in between, you resort to the SDS.This pertains to both gen sets.
 
slect said:
Ok, Bond both gen sets as seperately derived systems. Run 3-wire (phase conductors) to 3-pole transfer switch. No Equipment Grounding conductor to Transfer Switch.
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Select, no grounded conductor (neutral) to the transfer switch.You run a ground wire from the gen set to the transfer switch.

slect;980878) said:
Install 3-wire to Transformer with an EGC. Bond as a seperately derived system.
Install 4 wire with an EGC from transformer to MDP. No System Bond at MDP.
Click to expand...
Correct
 
I have read thru this thing, and for the life a me I can not figure out what the issue with bonding both generators and running four wires thru xfer switch to MDP. Floating the grounded conductor after generators, like what was first suggested. What am I missing?
 
mistermudd said:
I have read thru this thing, and for the life a me I can not figure out what the issue with bonding both generators and running four wires thru xfer switch to MDP. Floating the grounded conductor after generators, like what was first suggested. What am I missing?
Click to expand...


The neutral and ground are in parallel with each other. The ground wire will carry current along with the neutral.
 
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