Does there need to be an equipment ground?

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JdoubleU

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The primary side of this transformer is 12,470 and the secondary is a three phase 120/208 Y. The transformer feeds two 400 amp MDPs. The neutral is bonded at the transformer and at the 400 amp MDPs. Both of the 400 amp MDPs Have neutral loads so there is a Neutral at them. Does there need to be an equipment ground pulled to both MDPs from the transformer or would that create a parallel path?
 
If this is a POCO transformer, then one bond at the secondary and one at each MDP might be OK. With only a neutral and no EGC to each MDP.
But if it is a customer transformer wired as a Separately Derived System there should be an EGC between transformer and each MDP and there should only be one bond, at the transformer.
 
If this is an utility transformer then the main bonding jumper is installed at the service disconnect and no additional conductor is used. If this is a facility owned transformer then a supply side bonding jumper will be required between the transformer and the first disconnect.
 
Aside from other mentions, is this a new or existing installation? If existing, under what Code cycle was it installed?

I'm asking because several cycles ago, a supply-side bonding jumper was not required for SDS (i.e facility owned).
 
If is is not a POCO transformer (and therefore not a service) then it is a separately derived system according to NEC.

If it is a separately derived system you can not bond the grounded conductor at both the transformer and at the first disconnect unless there is no other conductive paths between the two as that does create parallel paths for grounded conductor current to flow.
 
Would the supply side boning Jumper only be required if a neutral is not being used example would be only 208 3 phase loads. But since there is a neutral, only a equipment ground is needed. And in this case we could remove the bonding jumper at the transformer and run a equipment ground and do all the bonding at the services.


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JdoubleU said:
Would the supply side boning Jumper only be required if a neutral is not being used example would be only 208 3 phase loads. But since there is a neutral, only a equipment ground is needed. And in this case we could remove the bonding jumper at the transformer and run a equipment ground and do all the bonding at the services.


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Is this a service or a separately derived system? If it is a service you only need the neutral. If it is a SDS you need a supply side bonding jumper and if there are line to neutral loads you will also need a neutral.
 
Smart $ said:
Aside from other mentions, is this a new or existing installation? If existing, under what Code cycle was it installed?

I'm asking because several cycles ago, a supply-side bonding jumper was not required for SDS (i.e facility owned).
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The term "supply side bonding jumper" is fairly new, but a conductor serving that purpose has always been required, unless the installation permitted bonding of the neutral at both the transformer and the first disconnect. This conductor would have been required by 250.4.
 
Ok got it. Is it permitted by code to bond the neutral at both ends. If not (tell me if I a wrong) I would need to remove the bond at the transformer or MDP and run the supply side bonding jumper.


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JdoubleU said:
Ok got it. Is it permitted by code to bond the neutral at both ends. If not (tell me if I a wrong) I would need to remove the bond at the transformer or MDP and run the supply side bonding jumper.


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I think the point would be that if there is no EGC or SSBJ or whatever it might be called today, then you almost have to bond the neutral at both ends, but that is no longer permitted.
 
petersonra said:
I think the point would be that if there is no EGC or SSBJ or whatever it might be called today, then you almost have to bond the neutral at both ends, but that is no longer permitted.
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2014 added an exception to 250.30(A)(2)...
Exception: A supply-side bonding jumper shall not be required
between enclosures for installations made in compliance
with 250.30(A)(1), Exception No. 2.
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250.30(A)(1)...
Exception No. 2: If a building or structure is supplied by a
feeder from an outdoor transformer, a system bonding
jumper at both the source and the first disconnecting means
shall be permitted if doing so does not establish a parallel
path for the grounded conductor. If a grounded conductor
is used in this manner, it shall not be smaller than the size
specified for the system bonding jumper but shall not be
required to be larger than the ungrounded conductor(s).
For the purposes of this exception, connection through the
earth shall not be considered as providing a parallel path.
Click to expand...
 
petersonra said:
I think the point would be that if there is no EGC or SSBJ or whatever it might be called today, then you almost have to bond the neutral at both ends, but that is no longer permitted.
Click to expand...

Ok, that makes since. Does 250.24C apply to this situation and would that permit the grounded conductor to be bonded at both end and be used as a ground fault current path?
 
JdoubleU said:
Ok, that makes since. Does 250.24C apply to this situation and would that permit the grounded conductor to be bonded at both end and be used as a ground fault current path?
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250.24 only applies to "service" supplied systems.

The rules are different for service supplied systems and separately derived systems. That is why you have been asked to tell us what type of system you have.
 
don_resqcapt19 said:
250.24 only applies to "service" supplied systems.

The rules are different for service supplied systems and separately derived systems. That is why you have been asked to tell us what type of system you have.
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Its a privately owned utility. I believe by definition a service is where the utility and the owner meet. So even though in most cases this transformer would be a service, by definition its just a separately derived system because we own it.
 
JdoubleU said:
Its a privately owned utility. I believe by definition a service is where the utility and the owner meet. So even though in most cases this transformer would be a service, by definition its just a separately derived system because we own it.
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In that case, assuming this is a new installation, you are not permitted to bond the neutral at both the transformer and the first disconnect. Primary distribution systems are common for industrial or campus type installations and the rules in 250.30 and 250.32 apply to your installation. The rules in 250.24 do not.
 
don_resqcapt19 said:
In that case, assuming this is a new installation, you are not permitted to bond the neutral at both the transformer and the first disconnect. Primary distribution systems are common for industrial or campus type installations and the rules in 250.30 and 250.32 apply to your installation. The rules in 250.24 do not.
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See post #11 above for where/when it is permitted under 2014 Code — pertinent edition for this installation has not been established in this thread thus far.
 
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