bonding generators and mts

[ericlau]

My situation is this. Am installing a power grid on small Army base in Afghanistan. I have 2 416 kw gensets and 1200 amp mts. I will be installing a delta ground system and would like bond neutral at mts. The neutral is bonded to frame of gensets now should I, a.romove bond at gensets b.leave it be or c.attach ground system to gensets.

 

[LarryFine]

If the T/S switches the neutral, the bond should be at the source. If it does not, the bond should be at the T/S.

It should never be in both places.

 

[benaround]

My situation is this. Am installing a power grid on small Army base in Afghanistan. I have 2 416 kw gensets and 1200 amp mts. I will be installing a delta ground system and would like bond neutral at mts. The neutral is bonded to frame of gensets now should I, a.romove bond at gensets b.leave it be or c.attach ground system to gensets.

Are these gensets the primary power for the grid ? Gensets have neutrals, so

what is a delta ground system ? Doesn't the Army have specs on how to

install this type of equipment ?

 

[jrannis]

Ignore the bond inside of the generator.

Connect the ground at the MTS neutral if is considered your "Service" disconnect.
Connect an equipment ground to the frame of the generator and connect it to your MTS enclosure.

Its possible that someone could bring in a generator that doesnt have the neutral connection inside of the generator.

 

[LarryFine]

Ignore the bond inside of the generator.

I don't think you can bond at both the generator and the T/S.

If you can, that means my last post is wrong; we can't have that.

 

[RUWired]

Ignore the bond inside of the generator.

Connect the ground at the MTS neutral if is considered your "Service" disconnect.
Connect an equipment ground to the frame of the generator and connect it to your MTS enclosure.

.

The bonding jumper has to be made between the SDS and the first OCPD.Conductors have to be protected at the point where they recieve there supply, so either the generator or the MTS will need OCP and that will determine the location of the jumper.

Rick

 

[jrannis]

You have to ensure that the building is properly wired.
You cant be sure of what kind of equipment someone might roll up with or who will be asked to connect it to the building.
Its best to check the frequency, voltage, breaker size and KW of the unit along with the rotation if necessary and not be overly concerned about how the netural is connected to the generator head.
It will not matter to you.

 

[George Stolz]

I don't think you can bond at both the generator and the T/S.

If you can, that means my last post is wrong; we can't have that.

I think it was right, Larry - I got your back.

 

[RUWired]

I think it was right, Larry - I got your back.

George, i couldn't back Larry up with his statement that the type of transfer switch determined the location of the bonding jumper. The O.P. has two generators feeding one transfer switch. In this case the location of the ocpd detemines the location. If the neutral is switched or not, is not a factor.

Rick

 

[George Stolz]

Hang on, I need to grab something so I can play along:

How do we know that the two generators are the two different sources connected to the MTS?

Edit to add: It would help to see a one-line to understand what we are offering advice on in this. I think we're all seeing different installations based on the information given.

 

[jrannis]

Hang on, I need to grab something so I can play along:

How do we know that the two generators are the two different sources connected to the MTS?

Edit to add: It would help to see a one-line to understand what we are offering advice on in this. I think we're all seeing different installations based on the information given.

I have 2 416 kw gensets and 1200 amp mts.

How bout that their OP third sentence?

 

[RUWired]

How do we know that the two generators are the two different sources connected to the MTS?

Am installing a power grid on small Army base in Afghanistan.

I have 2 416 kw gensets and (missing A)1200 amp mts.

I will be installing a delta ground system and would like bond neutral at mts.
.

As soon as they improve this fiber optic, we'll be able to see what the OP is saying. But untill then i am only assuming that he is installing a new grid with two gen sets and one transfer switch.

Rick

 

[George Stolz]

As soon as they improve this fiber optic, we'll be able to see what the OP is saying.

But untill then i am only assuming that he is installing a new grid with two gen sets and one transfer switch.

Rick

I was thinking about this on the way out, and there's just a lot of different ways to see it. I do apologize for saying you guys were jumping to conclusions, that was not cool.

The two different ways I can see this are two generators connected to a pole of the MTS, and some kind of utility power connected to the other pole. The other is two generators connected to either pole of the MTS, which could change things too.

Lately I've been dealing with a lot of redundancy, and so a pair of generators on the same pole wouldn't have surprised me - but in retrospect, you guys are probably right about the configuration.

So, starting at the top:

Gensets have neutrals, so what is a delta ground system?

The only use of that term I know of is the practice of driving three ground rods in close proximity to each other in a triangular pattern. I don't see the relevance here, unless the OP intends to connect to drive one set of these rods at the MTS and call it a day, to avoid driving rods at the generators.

If we assume that both generators are two different SDSs that supply the MTS, and also assume that OCPD is present at the generators before they feed the transfer switches, then I would say that is the reverse of what's required in the NEC. 250.30(A)(7)(x.1) would require the rods be connected at each generator, at the disconnecting means provided. Grounding electrodes at the MTS would not be required, unless we consider it screwed to a detached structure governed by 250.32(A).

If we were to assume they are two SDSs, then the neutrals would have to be switched, and the bonding would take place in each generator. Each generator would be an SDS requiring a GES of their own.

If we were to consider the pair one SDS, then the neutrals could be connected together (but separate from the EGCs) inside the MTS. Then, one generator would retain it's bonding jumper and the other wouldn't. The generator with the bonding jumper in it would have a GES, and the other one wouldn't.

Ignore the bond inside of the generator.

I don't see how this is a code compliant approach.

Connect the ground at the MTS neutral if is considered your "Service" disconnect.

If there are one or two SDSs and no service, then there is no service disconnect. There is a disconnect required by 445.18 to be located in the generator. If there's a disconnect at the generator, then it would have to be ahead of the transfer switch, and that would eliminate the option of the SDS Grounding Electrode System (GES) originating at the MTS.

Its possible that someone could bring in a generator that doesnt have the neutral connection inside of the generator.

You cant be sure of what kind of equipment someone might roll up with or who will be asked to connect it to the building.
Its best to check the frequency, voltage, breaker size and KW of the unit along with the rotation if necessary and not be overly concerned about how the netural is connected to the generator head.
It will not matter to you.

We are not responsible for the grounding mistakes of those that come after this, and this is encouraging a 250.6 violation to protect against those mistakes, IMO.

That's my take on the situation, jumping into the conclusions game. Thoughts?

 

[LarryFine]

Is the generator's breaker considered the building's main disconnect, even if the building itself has its own main disconnect?

 

[iwire]

We are not responsible for the grounding mistakes of those that come after this, and this is encouraging a 250.6 violation to protect against those mistakes, IMO.

I agree, we have to install per code for the siuation today.

 

[jrannis]

The situation is that two sources of power are providing for one building.

The OP is using one MTS for the installation

Prepare the building for the service.
1. Install MTS and connect the neutral to the delta ground
2. Inspect and test the generators for compatibility with the building voltage
3. Connect to the building

Do not be concerned with what the neutral does before it enters the domain of the building. It does not matter to the building electrical system just as it does not matter what the POCO does at their transformer.

Answer b. Leave it be

 

[iwire]

Do not be concerned with what the neutral does before it enters the domain of the building. It does not matter to the building electrical system just as it does not matter what the POCO does at their transformer.

What happens on the POCO side of the service point is nothing to be concerned with. The NEC does not apply.

But the generator is on the customer supplied side of the service point and must comply with the NEC.

You can not choose to ignore the generator connections just because they are outside the 'domain of the building'.

 

[jrannis]

Bob,
This is an Army base in Afghanistan.

It isnt going to make a difference if its connected or not.
Some units have the neutral bolted to the alternator head, some dont.
It could run for a week and get moved and another unit brought in.
Protect the building,
Safest and most universal way it is to bond the MTS neutral to the delta ground and run 5 wires to each of the units.

 

[iwire]

Bob,
This is an Army base in Afghanistan.

He came to an NEC website asking what to do. IMO he deserves an NEC answer. And considering all the issues they have been having with electricity and service personal IMO no one should just be winging it. Follow the standard rules that work.

 

[iwire]

Safest and most universal way it is to bond the MTS neutral to the delta ground and run 5 wires to each of the units.

I would say the safest way is to do it right and if his gensets are bonded the above is incorrect.