Seperately derived system

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Hoggedy

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Gloucester,VA,USA
Hello I have a 75kva transformer stand being built with a disconnect switch (100A)(480V) feeding the primary side. I then have a 120/208v panel mounted to the other side of the transformer itself. The conductors going through the RMC will be supplying under 250v. I ran a EGC from inside the transformer to the ground bus in the panel. Also XO is bonded to ground inside the transformer.My question is, do I need a bonding bushing placed on the conduit connecting the transformer to the secondary side panel?
 
No bonding bushing required when the voltage is below 150 volts to ground. Just for clarity the conductor between the transformer is a SSBJ (supply side bonding jumper) not an EGC. That is distinction is important because SSBJ's are sized differently.
 
infinity said:
No bonding bushing required when the voltage is below 150 volts to ground. Just for clarity the conductor between the transformer is a SSBJ (supply side bonding jumper) not an EGC. That is distinction is important because SSBJ's are sized differently.
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If the connection between the secondary side of the xfmr to the panelboard is in RMC all the way, I don’t think the SSBJ was required?
 
rojay said:
If the connection between the secondary side of the xfmr to the panelboard is in RMC all the way, I don’t think the SSBJ was required?
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That is correct, the SSBJ could be a metal raceway in lieu of a wire type SSBJ as long as it qualifies as an EGC. Stick a piece of FMC on the end and then a wire type SSBJ is needed.
 
Clarification

Clarification

I have a co worker that is saying that a bonding bushing has to be placed on the RMC raceway inside the XMFR connecting the XFMR to the panel. I said that there is no need since there is no eccentric or concentric knockouts present. He claims they have been bonding the raceway for years. Is there somewhere in the code that says bonding the raceway is not required just so I can show him?
 
Hoggedy said:
I have a co worker that is saying that a bonding bushing has to be placed on the RMC raceway inside the XMFR connecting the XFMR to the panel. I said that there is no need since there is no eccentric or concentric knockouts present. He claims they have been bonding the raceway for years. Is there somewhere in the code that says bonding the raceway is not required just so I can show him?
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The way the NEC is written it would say that it's required if it actually was not the other way around. Ask him for a code reference, you might have to wait a while for him to find it because it doesn't exist.

Doing something a certain way for years does not make it a code requirement but there's nothing wrong with exceeding what the NEC requires.
 
infinity said:
The way the NEC is written it would say that it's required if it actually was not the other way around. Ask him for a code reference, you might have to wait a while for him to find it because it doesn't exist.

Doing something a certain way for years does not make it a code requirement but there's nothing wrong with exceeding what the NEC requires.
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I understand doing extra is always okay. He claimed that I had to do it because code says so. If he was right I would have to go back and fix the other 4 transformer stands I already built. That was why the answer was critical. I appreciate it. The answer is, No I do not have to bond the raceways. thank you
 
So, I was told to look at 250.92 services. where it states that normally non current carrying metal parts shall be bonded together.
So I think the issue here is dictating whether or not this is considered a service or a separately derived system.
The conductors feeding the disconnect are going to be fed from a cable that will then be connected to a Meltric on the side of a breaker panel. The breaker (branch circuit) will feed the cable, in turn feeding the switch(primary side of transformer) and then the secondary side will feed another panel.
wouldn't a service only be the wires between the serving utility and the service equipment? making the service only the points where it enters our company? everything downstream of that is feeders and branch circuits? in turn, a branch circuit feeds our switch to transformer, making that a separately derived system. Which would make it not necessary to bond the raceways?
How do I distinguish what is a service and what is a SDS bonding raceways changes based on which one we are dealing with.
 
Hoggedy said:
So, I was told to look at 250.92 services. where it states that normally non current carrying metal parts shall be bonded together.
So I think the issue here is dictating whether or not this is considered a service or a separately derived system.
The conductors feeding the disconnect are going to be fed from a cable that will then be connected to a Meltric on the side of a breaker panel. The breaker (branch circuit) will feed the cable, in turn feeding the switch(primary side of transformer) and then the secondary side will feed another panel.
wouldn't a service only be the wires between the serving utility and the service equipment? making the service only the points where it enters our company? everything downstream of that is feeders and branch circuits? in turn, a branch circuit feeds our switch to transformer, making that a separately derived system. Which would make it not necessary to bond the raceways?
How do I distinguish what is a service and what is a SDS bonding raceways changes based on which one we are dealing with.
Click to expand...

An SDS has similar requirements regarding GEC's and bonding jumpers but it is not the same as a service. As Dave stated the definitions and distinctions between the two start in Article 100.

For the record I still have guys telling me (incorrectly) that you need bonding bushings on a transformer because you "treat it like a service".
 
The definition of service has always confounded a lot of people when it comes to industrial complexes where the service point is typically at a main substation and all the supplies to the buildings are then feeders and separately derived systems. As was mention earlier, there grounding requirements for services and other supplies are similar but not exactly the same. I have a few documents that I developed for my site to help our workers understand the differences. One shows the changes to the definition of services over the last 10 or so code cycles, one illustrates what constitutes a service, and one is a comparison of the code requirements for services to those for feeders and SDS's. They are too big to share as attachments but I am happy to share via email if you PM me your email address. It might help in discussions with your peers.
 
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