service entrance conduit

[elec58]

Trying to understand bonding of service conduit. For instance if I install EMT from an SDS to a panel board I am required to bond the EMT at one end. Question#Is a bond required if I pull an SSBJ with the grounded conductor ?
Also if it is required why isn't it required to bond EMT to downstream panel boards? TIA

 

[Dennis Alwon]

The emt must be bonded between the separately derived system and the first means of disconnect. Once you leave the service equipment then the emt doesn't need a bonding jumper.

 

[elec58]

The emt must be bonded between the separately derived system and the first means of disconnect. Once you leave the service equipment then the emt doesn't need a bonding jumper.

My reason for the question is why, I don't understand why a service conduit needs to be bonded and conduits to panels down stream dont. The SSBJ bonds the SDS to the main panel, if the purpose of the bond to the service conduit is to clear a fault if the conduit gets energized, why not require on all sub panels that have metallic conduit as raceways?

 

[ActionDave]

My reason for the question is why, I don't understand why a service conduit needs to be bonded and conduits to panels down stream dont. The SSBJ bonds the SDS to the main panel, if the purpose of the bond to the service conduit is to clear a fault if the conduit gets energized, why not require on all sub panels that have metallic conduit as raceways?

Your mixing the terms Service and SDS. While they are similar they are not the same. A piece of EMT between a POCO meter and the first disconnect has to bonded at one end because it's the one place where you are required to carry neutral current on the metal parts. The meter base is solidly bonded to the neutral, the first disconnect is solidly bonded to the neutral and we want to make sure that any EMT in between can't be floating under any circumstances.

 

[elec58]

Your mixing the terms Service and SDS. While they are similar they are not the same. A piece of EMT between a POCO meter and the first disconnect has to bonded at one end because it's the one place where you are required to carry neutral current on the metal parts. The meter base is solidly bonded to the neutral, the first disconnect is solidly bonded to the neutral and we want to make sure that any EMT in between can't be floating under any circumstances.

OK so carrying the neutral current is the issue Thanks for the clarity.

 

[kwired]

All metal raceways must be bonded to either EGC or grounded service conductor if on supply side of service disconnecting means.

250.92(B) says "Standard locknuts or bushings shall not be the only means for the bonding", and is reason why we often use additional bonding jumpers or specialty fittings for service raceways.

Standard locknuts are acceptable bonding method for many other places that do not involve service conductors.

 

[tom baker]

Trying to understand bonding of service conduit. TIA

The electrician term for this is "unfused service entrance conductors". The overcurrent protection is on the primary side of the POCO transformer.
The definition of overcurrent says "it may result from overload, short circuits or ground faults". Service conductors are only protected from overloads, as you have done a load calculation on the service. There is no protection against short circuits and ground faults except by the POCO fuse on the primary.
There are three parts to the protection of unfused conductors
1. Additional bonding
2. Restriction on the type of raceway allowed
3. Distance the raceway can go in a building

In Washington we can't use SE cable or EMT, and the distance is limited to 15 ft of raceway, by state rules. Some pocos may require Sch 80 PVC.

once you are past the service, you are using the rules for feeders or branch circuits and since you have short circuit and ground fault protection, additional bonding is typically not required (but are for 480V and hazardous locations)

 

[kwired]

The electrician term for this is "unfused service entrance conductors". The overcurrent protection is on the primary side of the POCO transformer.
The definition of overcurrent says "it may result from overload, short circuits or ground faults". Service conductors are only protected from overloads, as you have done a load calculation on the service. There is no protection against short circuits and ground faults except by the POCO fuse on the primary.
There are three parts to the protection of unfused conductors
1. Additional bonding
2. Restriction on the type of raceway allowed
3. Distance the raceway can go in a building

In Washington we can't use SE cable or EMT, and the distance is limited to 15 ft of raceway, by state rules. Some pocos may require Sch 80 PVC.

once you are past the service, you are using the rules for feeders or branch circuits and since you have short circuit and ground fault protection, additional bonding is typically not required (but are for 480V and hazardous locations)

You may have local restrictions, NEC only prohibits FMT and ENT to be used for service conductors.