Additional Ground Rods?

[hoyt]

My shop has 208 3-phase 400 amp service. I have two main breaker panels, one of which is 3-phase and two remote 100 amp single phase sub-panels. There is only one ground rod at the main panel; I've cleaned the rod and replaced the clamp.. The ground and neutral busses are bonded together in all the panels. None of the existing circuits use a dedicated ground wire, instead using the EMT as ground. The electrical system was last updated 40 years ago. Every 120V duplex outlet was crumbling from age, so I've replaced them all. Should I add additional ground rods at the sub-panels?

 

[gnxtc2]

The neutral and grounds are bonded in the main panel. The neutral in the sub panel must not be bonded. The grounds and neutrals in the sub panels must be isolated from each other.

No, do not add ground rods to the sub panels. You could add an additional ground rod at the main panel if the resistance is above 25 ohms.

Billy T.
[email protected]

 

[RivennHewn]

Two rods, 8 feet apart is code where I work.

 

[matt151617]

Is the shop detached? If so, it needs it's own ground rods. Otherwise, nothing says you can't add additional ones to what you have now, but you'll have to run new copper from the panel... splices aren't allowed.

 

[Speedy Petey]

Just so you know. Ground rods have NOTHING to do with circuit grounding and equipment grounds. Equipment grounding comes from the neutral bond in the main panel. The neutral coming in from your utility serves as both the neutral and the equipment ground.

Ground rods serve and entirely different purpose, and don't really do much at all.
Are you sure that the two 100A panels are sub-panels and not two additional main panels?
Where do they originate? Are there main breakers in the panels?

 

[sparky36000]

Is the shop detached? If so, it needs it's own ground rods. Otherwise, nothing says you can't add additional ones to what you have now, but you'll have to run new copper from the panel... splices aren't allowed.

Splices are allowed by NEC. 250-64(C)

(C) Continuous. Except as provided in 250.30(A)(5) and
(A)(6), 250.30(B)(1), and 250.68(C), grounding electrode
conductor(s) shall be installed in one continuous length
without a splice or joint. If necessary, splices or connections
shall be made as permitted in (1) through (4):
(1) Splicing of the wire-type grounding electrode conductor
shall be permitted only by irreversible compressiontype
connectors listed as grounding and bonding equipment
or by the exothermic welding process.
(2) Sections of busbars shall be permitted to be connected
together to form a grounding electrode conductor.
(3) Bolted, riveted, or welded connections of structural
metal frames of buildings or structures.
(4) Threaded, welded, brazed, soldered or bolted-flange
connections of metal water piping.

 

[wyliesdiesels]

My shop has 208 3-phase 400 amp service. I have two main breaker panels, one of which is 3-phase and two remote 100 amp single phase sub-panels. There is only one ground rod at the main panel; I've cleaned the rod and replaced the clamp.. The ground and neutral busses are bonded together in all the panels. None of the existing circuits use a dedicated ground wire, instead using the EMT as ground. The electrical system was last updated 40 years ago. Every 120V duplex outlet was crumbling from age, so I've replaced them all. Should I add additional ground rods at the sub-panels?

One ground rod was all that was required back when your shop was built. So don't worry about adding another ground rod to your main service panel. And for 400a service I believe it's suppose to be a 5/8" rod. The sub-panels only require rods if they're @ a detached building. And as 'speedy' said, ground rods serve a different purpose than an EGC(equipment grounding conductor). Using EMT as the EGC is fine as long as there's a solid connection back to the panel. Also, if the panels you're calling sub-panels really are subs, then u need to remove the neutral to ground bond and make sure the neutral bus bar is isolated/insulated from the panel.