equipment grouding

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mull982

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I am working on a project which has a conveyor that has a 25hp 480V motor being fed from a 50A breaker. The motor feeders going to this motor are a
3/C #6 w/gnd. Since the motor is sitting on a stell conveyor structure I am looking at having to equipment ground the conveyor structure.

My question is, weather or not I have to look at table 250.122 and run a #10 equipment grounding conductor (using 60A overcurrent device rating from table) from the MCC to the conveyor structure. Is it possible to just use the ground wire that is running with the motor feeds and bond it to the conveyor structure or do I need a seperate equipment ground conductor for this instance.
 
mull982 said:
I am working on a project which has a conveyor that has a 25hp 480V motor being fed from a 50A breaker. The motor feeders going to this motor are a
3/C #6 w/gnd. Since the motor is sitting on a stell conveyor structure I am looking at having to equipment ground the conveyor structure.

My question is, weather or not I have to look at table 250.122 and run a #10 equipment grounding conductor (using 60A overcurrent device rating from table) from the MCC to the conveyor structure. Is it possible to just use the ground wire that is running with the motor feeds and bond it to the conveyor structure or do I need a seperate equipment ground conductor for this instance.
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why would you need to run an additional #10 when you already have a #6 there?
 
equip grnd

equip grnd

If i understand you correctly that you have a #6 grnd running with the feed conductors i dont see any reason to run another #10 with it. just use the #6 grnd as your equipment ground.
 
petersonra said:
why would you need to run an additional #10 when you already have a #6 there?
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I think that the OP means that he has (3) #6 (hot) conductors and a #10 cu grounding conductor in the motor circuit.

Either way, the #10 motor circuit grounding conductor should work to ground the (60A) motor and framing, another grounding conductor shouldn't be necessary.

Is the motor isolated (insulated) from the framing?
Is this the only motor?

steve
 
hillbilly said:
I think that the OP means that he has (3) #6 (hot) conductors and a #10 cu grounding conductor in the motor circuit.

Either way, the #10 motor circuit grounding conductor should work to ground the (60A) motor and framing, another grounding conductor shouldn't be necessary.

Is the motor isolated (insulated) from the framing?
Is this the only motor?
Click to expand...

This is correct. I have (3) #6 hot conductors with a #10 ground going to the motor. The motor is not insulated from the steel conveyor structure rather it is just bolted to the structure. My queststion was weather or not I needed a ground conductor for the actual conveyor structure to ground it? In other words I know my motor equipment ground is covered by the #10 ground going to it, but was not sure about the actual conveyor structure.

This is the only motor on the conveyor, however there are 120V controls at different points along the conveyor. These controls and motor feeds will most likely be run in cable tray.
 
If the motor is solidly bonded (bolted) to the metal conveyor framing, the motor circuit grounding conductor will also bond the framing.

Let me make sure that I've got this right....

You have a solid metal frame with a grounded motor securely mounted on it with metal to metal contact?

If so...in my opinion... you don't need another grounding conductor for the framing.
It will be grounded (bonded) thru the motor circuit.
Read 250.32(1), 250.122, 250.130, 250.134 and 250.136(A).

steve
 
Let me ask another question similarly related to this topic. With conductors feeding from a transformer to an MCC would the grounding conductors with these conductors (say 4 sets of 500MCM as an example) be considered equipment grounding conductors or service grounding conductors. The transformer is a 4160/480 xfmr feeding a 480V MCC. Which table in NEC section 250 would I have to reference to size these conductors?
 
mull982 said:
Let me ask another question similarly related to this topic. With conductors feeding from a transformer to an MCC would the grounding conductors with these conductors (say 4 sets of 500MCM as an example) be considered equipment grounding conductors or service grounding conductors. The transformer is a 4160/480 xfmr feeding a 480V MCC. Which table in NEC section 250 would I have to reference to size these conductors?
Click to expand...

Their only considered services ahead of the service disconnect everything downstream past the service disconnect is distribution/premises wiring.

Yours are feeders (unless the transformer is utility owned), and your equipment grounding is as per 250-30 and you will be using table 250-66
 
tryinghard said:
Their only considered services ahead of the service disconnect everything downstream past the service disconnect is distribution/premises wiring.

Yours are feeders (unless the transformer is utility owned), and your equipment grounding is as per 250-30 and you will be using table 250-66
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So you are saying that the 4 ground wires running with the 4 sets of parallel feeds from a transformer to an MCC are equipmnet gound conductors and should be sized per table 250.66? We have a substation on-site with the utility transformer. After this transformer, you are saying that all the grounds running with the distribution feeders throughout the plant are considered equipment grounds?
 
mull982 said:
So you are saying that the 4 ground wires running with the 4 sets of parallel feeds from a transformer to an MCC are equipmnet gound conductors and should be sized per table 250.66? We have a substation on-site with the utility transformer. After this transformer, you are saying that all the grounds running with the distribution feeders throughout the plant are considered equipment grounds?
Click to expand...

Table 250.66 is for GEC. Table 250.122 is for EGC which would be based on the size of the OCD.

In your case it sounds like you need to use 250.122, not 250.66
 
I guess before I get my hands around this whole grounding thing and as I read through section 250 of the NEC I have to understand the terminology. I was hoping someone could help me with the terminology for the different section of the power distribution system in my plant.

We own our substation where the utility comes in at 230kV and connects to a 230kv to 4.16kv main transformer. From this main transformer we have 4.16kv feeders feeding a main lineup of 5kV main switchgear. This switchgear feeds several 4.16kV to 480/277 transformers around the plant. These transformers then serve 480V MCC's.

In my plant what would be considered the service. (referencing 250.24 stating that an ECG needs to be connected at every "service") Would my main substation be considered the service, or would the main lineup of 5kV switchgear be considered the service? Is there multiple "services" in my distribution system? What would all of the other transformers and MCC's be considered? What would be my service conductors?

Thanks for all the help.

Mull982
 
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