bonding CT can

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michaelstanley

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An overhead 800A 3Ph 208/120 service with ct can with a lateral to service equipement inside building. I see a #4 bare cu. coming out of the ctcan to a gr. rod/s. I am going to mount a transfer sw. at the ct location and have questions. 1) How do you properly connect lug to ct can for a bonding jumper in this case?), ( I have just used short bolt with lock washer and nut in the past). 2)Should the bonding jumper between the ct can and the Trans. Sw. be a 2/0 cu. and 3) Do I need to use the ground rods already installed here with the #4 bare cu. ????
 
Re: bonding CT can

Is this transfer switch also the service disconnect?

If so use the neutral as the bonding jumper.

Please explain the layout more.

[ August 19, 2004, 04:46 PM: Message edited by: iwire ]
 
Re: bonding CT can

As i understand it the bond has to be sized to the gec size or is this a poco thing
 
Re: bonding CT can

Overhead service to ct can, service lateral to building mechanical room to service equipement. I am going to add a manual transfer (double throw) switch at the location of the ct can and refeed the building from the transfer switch. I am not sure you would call it a service disconnect, but I still have three questions. Another question would be, What is the #4 bare cu. coming from the ct can to a ground rod?? Shouldn't the grounding electrode be in the mech room with the service equipement??
 
Re: bonding CT can

Sorry about that. The service is 2 parallel sets of 500kcmil cu thhn. Yes I woud think that the bond between the transfer sw. and the adjacent ct can would be required and sized at 2/0 cu.
Normally the service conductors would feed straight from the service mast right thru the ct can to the service equipement in the mech room. I will need to break all conductors at the switch now, including the neutral. This switch comes with a neutral assembly and a ground kit. I plan to jump a bond from switch to ct can. Do I need to still tie in to the existing gr. rod/s?
 
Re: bonding CT can

I am not trying to ignore your questions but unless I am misunderstanding your layout you have a much larger problem. Please look at the following code sections and compare them to what you plan on doing.

230.91 Location.
The service overcurrent device shall be an integral part of the service disconnecting means or shall be located immediately adjacent thereto.
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230.94 Relative Location of Overcurrent Device and Other Service Equipment.

The overcurrent device shall protect all circuits and devices.

Exception No. 1: The service switch shall be permitted on the supply side.

Exception No. 2: High-impedance shunt circuits, surge arresters, surge-protective capacitors, and instrument transformers (current and voltage) shall be permitted to be connected and installed on the supply side of the service disconnecting means as permitted in 230.82.

Exception No. 3: Circuits for load management devices shall be permitted to be connected on the supply side of the service overcurrent device where separately provided with overcurrent protection.

Exception No. 4: Circuits used only for the operation of fire alarm, other protective signaling systems, or the supply to fire pump equipment shall be permitted to be connected on the supply side of the service overcurrent device where separately provided with overcurrent protection.

Exception No. 5: Meters nominally rated not in excess of 600 volts, provided all metal housings and service enclosures are grounded in accordance with Article 250.

Exception No. 6: Where service equipment is power operable, the control circuit shall be permitted to be connected ahead of the service equipment if suitable overcurrent protection and disconnecting means are provided.
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As you can see a standard transfer switch is not one of the exceptions listed and is not allowed on the supply side of the service disconnect / overcurrent protection.

Exception 5 is what allows the CT can on the supply side of the overcurrent protection.

I think you can get transfer switches that are service rated with built in overcurrent protection and can manually open the service conductors. This switch would become the service switch. Then you would also have to remove the original main bonding jumper and run all your GECs to this service rated transfer switch.

That aside back to your question.

Any bonding conductors needed on the supply side of the service switch are sized by Table 250.66

Two sets of 500 copper = 1000 Kcmil so you would need a 2/0 copper or a 4/0 aluminum.

Bob

[ August 20, 2004, 05:58 AM: Message edited by: iwire ]
 
Re: bonding CT can

Iwire: I think you are right. When I add the Transfer switch, then the service entrance conductors start at the weather head and end at the line side of the transfer switch.
The Chief inspector said no protection necessary because the conductors enter the building at the (now existing) service equipement, which has an 800 amp main breaker.If the transfer switch was mounted to the building and the conductors feeding the now existing service equipement traveled through the building ,THEN overcurrent protection would be required. I'm stil looking. I found it? 240.21 (B)(5) No oc device required

[ August 20, 2004, 09:51 PM: Message edited by: michaelstanley ]
 
Re: bonding CT can

michael,
230.91 as pointed out by Bob, will require oevercurrent protection at the transfer switch (service disconnect). Nothing in 240 changes this requirement.
Don
 
Re: bonding CT can

What about exception #1 that says that the service switch can be on the supply side of the overcurrent device. If the transfer switch becomes the service switch and the overcurrent device is immediatly at the entrance of the conductors to the building, then that seems to meet exception #1. Back to what Iwire said about Transfer switch not being mentioned, Why could it not be regarded as a service switch. It does have an OFF position and is service rated with grounding kit installed.

[ August 20, 2004, 11:04 PM: Message edited by: michaelstanley ]
 
Re: bonding CT can

ALSO..... The existing Paralleled conductors have only the 3 ungrounded and 1 grounded conductor. This is ok as exists, but either way with fused or unfused Transfer switch wouldn't an equipement grounding conductor be required and then seperate what is now connected together at the service equipement IN the building?????
This stuff can get kind of complicated.

[ August 20, 2004, 11:44 PM: Message edited by: michaelstanley ]
 
Re: bonding CT can

Originally posted by michaelstanley:
What about exception #1 that says that the service switch can be on the supply side of the overcurrent device. If the transfer switch becomes the service switch and the overcurrent device is immediatly at the entrance of the conductors to the building, then that seems to meet exception #1.
Click to expand...
The switch would have to be listed as "Service Equipment" 230.66

IMO having the switch outside and the overcurrent protection inside does not come close to the "immediately adjacent" requirement of 230.91.

As to the grounding conductor yes it can get complicated.

In as short as I can put it, on the supply side of the service disconnect the neutral is what you want to use to bond the metal enclosures, I am sure the neutral is already bonded to the CT can.

If the transfer switch does become the service disconnect you will bond the neutral to that enclosure also.

I would use PVC between the CT can and the service disconnect and you will not have to bond anything, the CT and the service disconnect will already be bonded to the neutral.

If you run metal pipe between these two enclosures you will have to bond the metal pipe.

Do not run a grounding conductor between the CT can and the service disconnect, that will only be a parallel conductor to the neutral, a violation of 310.4

If the transfer switch becomes the service disconnect you will need a grounding conductor from there to the old service.

In this case you would have to remove the main bonding jumper in the old service disconnect and move the grounding electrodes from the old service disconnect out to the new service disconnect.
 
Re: bonding CT can

Hey Iwire, Do you know where the code speaks of the service conductors entering the building, I believe those are the words the inspector used??
The switch is service rated with ground kit installed, but unless I did what you said to run a EGC to the existing service equipement it would be unnecessary to install as the switch comes with a neutral assembly. I would want to install a EGC, although I would have to pull out and repull approx. 60 foot of the 500kcmil cu. (4 cond. 2 runs) What a job.

[ August 22, 2004, 12:13 AM: Message edited by: michaelstanley ]
 
Re: bonding CT can

I really appreciate every response. How about this for a final assesment. IF, the inspector concludes that the Transfer switch is immediately adjacent to the original service equipement in the mech room. Then just rearrange ct can with service masts, add transfer switch and bond ct can. IF NOT adjacent, THEN rearrange ct can and service masts, add fused disconnect, then transfer switch,(I haven't been able to locate a fused 800a 3 ph. tr. sw.) repull underground feeders with added EGC. Re-do ground rods and seperate neutrals and equipement grounding at mech room.

[ August 22, 2004, 12:11 AM: Message edited by: michaelstanley ]
 
Re: bonding CT can

Hi Michael, It all comes down to the AHJ all my comments are based on how I read the NEC, the AHJ may see things differently.

If it was me doing the job I would go with what the book spells out. If you do it the way the AHJ said you could then the AHJ comes out for inspection what is to stop the AHJ from 'forgetting' that they said it was OK. :(

The transfer switch needs overcurrent protection on the supply side of it, that applies if it is inside or outside the building.

I hate to do work twice and I am sure you do too, that is what I see happening if you go with the original plan.

Good luck with whatever way you decide.

Bob
 
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