3-phase delta service: size of neutral?

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sw_ross

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In sizing conductors for a 3-phase delta service that will have no neutral load I was assuming my neutral conductor size would only have to be not less than the GEC, 250.24(C)?

But then I saw 250.24(C)(3) Delta-Connected Service.
Says the neutral shall have an ampacity not less than the ungrounded conductors.

Am I reading this correctly? If so why does the neutral have to be sized that way?
My loads are all 3-phase 240 volt, they don't need a neutral.

Thanks
 
sw_ross said:
In sizing conductors for a 3-phase delta service that will have no neutral load I was assuming my neutral conductor size would only have to be not less than the GEC, 250.24(C)?

But then I saw 250.24(C)(3) Delta-Connected Service.
Says the neutral shall have an ampacity not less than the ungrounded conductors.

Am I reading this correctly? If so why does the neutral have to be sized that way?
My loads are all 3-phase 240 volt, they don't need a neutral.

Thanks
Click to expand...

A 3-phase, 3-wire delta service doesn't have a neutral.
 
sw_ross said:
In sizing conductors for a 3-phase delta service that will have no neutral load I was assuming my neutral conductor size would only have to be not less than the GEC, 250.24(C)?

But then I saw 250.24(C)(3) Delta-Connected Service.
Says the neutral shall have an ampacity not less than the ungrounded conductors.

Am I reading this correctly? If so why does the neutral have to be sized that way?
My loads are all 3-phase 240 volt, they don't need a neutral.

Thanks
Click to expand...

250.24(C)(3) refers to a 3 phase, 3 wire delta service. In that case you don't have a neutral but rather a grounded conductor.
I'm thinking you may mean that you have a 3 phase, 4 wire center tapped service which is a different animal.
 
Duh!..:slaphead:. Yeah, it is a 3-phase 240 volt with high leg.
Am I correct to say that all services had to be supplied with a neutral, not smaller than the 250.103(C)(1) table... I know a neutral isn't required for the planned loads.

Thanks
 
sw_ross said:
Duh!..:slaphead:. Yeah, it is a 3-phase 240 volt with high leg.
Am I correct to say that all services had to be supplied with a neutral, not smaller than the 250.103(C)(1) table... I know a neutral isn't required for the planned loads.

Thanks
Click to expand...

A grounded utility service that has a neutral must have the neutral brought to the service disconnect and bonded there. The neutral must be sized for the neutral load OR 250.102(C)(1) which ever is larger.
 
sw_ross said:
Duh!..:slaphead:. Yeah, it is a 3-phase 240 volt with high leg.
Am I correct to say that all services had to be supplied with a neutral, not smaller than the 250.103(C)(1) table... I know a neutral isn't required for the planned loads.

Thanks
Click to expand...
Grounded conductor must still be brought to the service equipment, even if it carries no current.

That said seems very likely there will be at least one 120 volt general use receptacle though.
 
Without the grounded conductor in play, do you actually have a wild leg. :)


JAP>
 
jap said:
Without the grounded conductor in play, do you actually have a wild leg. :)


JAP>
Click to expand...
If the source is grounded at midpoint of one phase, he still has 1.732 times more voltage to ground from the opposite corner of the delta than he has from the other two corners, whether he uses the "neutral" or not.

If a system is grounded we must bring the grounded conductor to the service disconnecting means.

We must extend EGC throughout the premises with wiring.

We don't need to extend the grounded conductor beyond the service equipment if there is no load that will utilize it.
 
jap said:
Without the grounded conductor in play, do you actually have a wild leg. :)


JAP>
Click to expand...
If the source is grounded at midpoint of one phase, he still has 1.732 times more voltage to ground from the opposite corner of the delta than he has from the other two corners, whether he uses the "neutral" or not.

If a system is grounded we must bring the grounded conductor to the service disconnecting means.

We must extend EGC throughout the premises with wiring.

We don't need to extend the grounded conductor beyond the service equipment if there is no load that will utilize it.

We only need to identify the high leg when the neutral is also present .
 
kwired said:
We only need to identify the high leg when the neutral is also present .
Click to expand...

I always identify it throughout the system, but, this makes me curious if it would be allowable not to identify it if only the EGC was present but not a Neutral or Grounded Conductor present?

JAP>
 
jap said:
I always identify it throughout the system, but, this makes me curious if it would be allowable not to identify it if only the EGC was present but not a Neutral or Grounded Conductor present?

JAP>
Click to expand...
From 110.15: "Such identification shall be placed at each point on the system where a connection is made if the grounded conductor is also present."

No grounded conductor, no chance of connecting that 120 volt load to the wrong ungrounded conductor, unless you are bootlegging neutral from an EGC.
 
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