Roll-up Generator Termination Box

[lielec11]

I am working on a job where we designed a generator to feed an emergency bus duct through a building from the roof down in New York City. The client has now requested we add to the job a "quick connect" point at the bottom of the bus duct for connection to a roll-up temporary generator, or a load bank.

I am looking at using Eaton's RUTGB (http://www.eaton.com/ecm/idcplg?IdcService=GET_FILE&dID=273282).

The load side of the box would be a permanent connection to the bottom of the bus duct via a fused disconnect switch located on the bus duct. The line side would temporarily connect to either a roll-up generator with a CB, or a load bank.

Does anyone see an issue with using this type of connection box without an OCPD in the box itself? My boss seems to think it will not be approved, however, myself along with the manufacturer think otherwise.

Thanks

 

[iwire]

Considering you do not know the size of the breaker the trailer mounted generator will have, how would you ensure proper overcurrent protection of the bus duct with out OCP at the connection point?

 

[Pharon]

I don't understand, if it's a fused disco, doesn't that qualify as OCPD?

 

[iwire]

I don't understand,

Apparently neither did I. I take back my comment.

 

[Pharon]

Not your fault. The OP's last paragraph is confusing...

 

[texie]

I am working on a job where we designed a generator to feed an emergency bus duct through a building from the roof down in New York City. The client has now requested we add to the job a "quick connect" point at the bottom of the bus duct for connection to a roll-up temporary generator, or a load bank.

I am looking at using Eaton's RUTGB (http://www.eaton.com/ecm/idcplg?IdcService=GET_FILE&dID=273282).

The load side of the box would be a permanent connection to the bottom of the bus duct via a fused disconnect switch located on the bus duct. The line side would temporarily connect to either a roll-up generator with a CB, or a load bank.

Does anyone see an issue with using this type of connection box without an OCPD in the box itself? My boss seems to think it will not be approved, however, myself along with the manufacturer think otherwise.

Thanks

You mention connecting a load bank. This would imply that there may be a permanently installed generator also connected to this bus. If so, how are you interlocking this?
For what it is worth, I think there are better generator connection boxes out there with all kinds of desirable options such as Cam-loks. I would also consider some type of phase rotation indication.

 

[lielec11]

Sorry for the confusion guys.

I don't understand, if it's a fused disco, doesn't that qualify as OCPD?

That is the point I am making. If there is a fused disconnect on the bus duct, why do I also need a fused disconnect in the termination box as well?

Considering you do not know the size of the breaker the trailer mounted generator will have, how would you ensure proper overcurrent protection of the bus duct with out OCP at the connection point?

The client will be limited to the size of roll-up generator they can use in this case based on the OCPD on the bus duct.

You mention connecting a load bank. This would imply that there may be a permanently installed generator also connected to this bus. If so, how are you interlocking this?
For what it is worth, I think there are better generator connection boxes out there with all kinds of desirable options such as Cam-loks. I would also consider some type of phase rotation indication.

Yes there will be a permanently installed generator on the roof per my original post. However, the point isn't to use both at the same time, so I don't believe there is any reason to provide phase rotation/paralleling equipment. The overcurrent protection device on the permanent genset will however be key-interlocked with the OCPD on the bus duct that will be used for the roll-up genset.

 

[Pharon]

That is the point I am making. If there is a fused disconnect on the bus duct, why do I also need a fused disconnect in the termination box as well?

So if I understand you correctly, you have a busduct fused switch with a feeder that goes to a termination box on the outside of the building somewhere for GRB cable terminations, correct?

If that's the case, how long is the run from the busduct to the termination box? And what OCPD will be protecting this run? With a roll up generator, the power will flow from the box to the busduct - this run needs to be protected, but would most likely be at the generator, assuming it has a main breaker.

 

[texie]

Sorry for the confusion guys.



That is the point I am making. If there is a fused disconnect on the bus duct, why do I also need a fused disconnect in the termination box as well?



The client will be limited to the size of roll-up generator they can use in this case based on the OCPD on the bus duct.



Yes there will be a permanently installed generator on the roof per my original post. However, the point isn't to use both at the same time, so I don't believe there is any reason to provide phase rotation/paralleling equipment. The overcurrent protection device on the permanent genset will however be key-interlocked with the OCPD on the bus duct that will be used for the roll-up genset.

I wasn't suggesting paralleling, rather just phase rotation indication so the less than skilled people connecting the portable machine get it right.
If you interlock with, say, Kirk keys how are you going to get power to the load bank?

 

[lielec11]

So if I understand you correctly, you have a busduct fused switch with a feeder that goes to a termination box on the outside of the building somewhere for GRB cable terminations, correct?

If that's the case, how long is the run from the busduct to the termination box? And what OCPD will be protecting this run? With a roll up generator, the power will flow from the box to the busduct - this run needs to be protected, but would most likely be at the generator, assuming it has a main breaker.

The run from the busduct to the termination box is approximately 60-80 feet of cable. In the case of a roll-up generator, the main breaker on the generator would protect the entire run from the roll-up gen to the busduct. In the case of a load bank, the fused disconnect on the busduct would protect the entire run from the disco to the load bank. Does this make sense?

 

[lielec11]

If you interlock with, say, Kirk keys how are you going to get power to the load bank?

That is a good point. At the very least, we'd have to provide a sign with a sequence of operation and provide lockable disconnect switch in lieu of kirk-keys. Thanks..

 

[Pharon]

In the case of a load bank, the fused disconnect on the busduct would protect the entire run from the disco to the load bank. Does this make sense?

So you'd be using the termination box for a temporary load bank connection, also? Is that what you're saying?

If so, then yes - your logic makes sense to me. As long as the fuse sizes in the busduct disconnect switch match the size of the feeder to the termination box.

Here's the only problem, though -- what if they bring in a bigger generator, with an OCPD larger than the size of that feeder? Then it wouldn't be protected.

If it's not too much trouble, you may want to consider just throwing in a fused disconnect switch right ahead of the termination box -- that way you cover the worst case scenario.

 

[Joe Villani]

The run from the busduct to the termination box is approximately 60-80 feet of cable. In the case of a roll-up generator, the main breaker on the generator would protect the entire run from the roll-up gen to the busduct. In the case of a load bank, the fused disconnect on the busduct would protect the entire run from the disco to the load bank. Does this make sense?

I would get some input from the DOB on this one.

I understand what you are doing but regardless of the cords, I am wondering if the DOB would consider this set up a "permanent connection for a portable generator"

If this is the case you would need a disconnect with overcurrent protection at the point of connection to the portable generator.

Take a look at NYC electrical code amendments 700.6(F) and (G) to make sure you're covered.

 

[Pharon]

Roll-up Generator Termination Box

Here's the only problem, though -- what if they bring in a bigger generator, with an OCPD larger than the size of that feeder? Then it wouldn't be protected.

If it's not too much trouble, you may want to consider just throwing in a fused disconnect switch right ahead of the termination box -- that way you cover the worst case scenario.

After thinking about this suggestion further, I've reconsidered. In the event that a bigger generator is used than what the feeder can handle, your busduct switch fuses will protect the feeder from an overload condition, and the generator output breaker (assuming it's a thermal-mag) would trip on a fault condition. So you're probably okay without OCPD at the termination box.

Though it wouldn't hurt to slap on a sign on the termination box saying how big the feeder is, and not to exceed it. Just for liability reasons. Bottom line is I don't know of anything in the Code that requires OCPD there. If an inspector demands it, ask him to cite the Code section.

 

[iwire]

I think it is bad design to count on an unknown variable (the genset breaker) to protect the conductors.

Having done a lot of temporary generator hook ups I can say I have never told the genset rental company what size breaker I need. I simply tell them I need a generator with minimum KW of X and we use what shows up.

It seems to me 240.21 applies.

240.21 Location in Circuit. Overcurrent protection shall
be provided in each ungrounded circuit conductor and shall
be located at the point where the conductors receive their
supply except as specified in 240.21(A) through (H). Conductors
supplied under the provisions of 240.21(A) through (H)
shall not supply another conductor except through an overcurrent
protective device meeting the requirements of 240.4.

That said you might be able to apply the tap rules to the conductors between the tap box and the bus duct.

As far as the ability of an AHJ to enforce this?

Easy

Inspector: What protects the conductors between the tap box and the bus duct?

Installer: The generator breaker.

Inspector: Where is the generator?

Installer: It is not here, it will brought in when needed.

Inspector: OK, call me back when you bring it in so I can issue you a final inspection, until that time this job is incomplete.

Installer: We need final long before that happens.

Inspector: Call me back when overcurrent protection is provided or show me what tap rules you think apply.

Inspector drives away .....

Real world gentlemen, not the internet.

 

[lielec11]

I think it is bad design to count on an unknown variable (the genset breaker) to protect the conductors.

Having done a lot of temporary generator hook ups I can say I have never told the genset rental company what size breaker I need. I simply tell them I need a generator with minimum KW of X and we use what shows up.

It seems to me 240.21 applies.



That said you might be able to apply the tap rules to the conductors between the tap box and the bus duct.

As far as the ability of an AHJ to enforce this?

Easy

Inspector: What protects the conductors between the tap box and the bus duct?

Installer: The generator breaker.

Inspector: Where is the generator?

Installer: It is not here, it will brought in when needed.

Inspector: OK, call me back when you bring it in so I can issue you a final inspection, until that time this job is incomplete.

Installer: We need final long before that happens.

Inspector: Call me back when overcurrent protection is provided or show me what tap rules you think apply.

Inspector drives away .....

Real world gentlemen, not the internet.

That is a good point regarding the actual ordering of a temporary generator, I'll keep that in mind. Thanks for the input on inspector comments as well. NYC Advisory Board is notorious for situations like this, so I should have thought about it more from the start.

 

[lielec11]

Take a look at NYC electrical code amendments 700.6(F) and (G) to make sure you're covered.

Thanks for this headsup. 700.6(G) looks like it requires a disconnecting means with an OCPD at the point of connection for the portable generator.

Thanks!