ECN Forum Forums General Topics of the Trade General Discussion Area Bonding and grounding

The OP said his only electrode was 2 rods.

Thanks for all the input and your help Guys. It just gets confusing on what to do when you have no building steel to use as a grid. Still not 100% on what to do.

You've got two grounding issues to contend with- fault clearing and bonding to the building ground.

Faults are cleared by current flowing through that fat green wire you pull in with your feed. At the service, the ground buss is bonded to the neutral buss, to return 'utility' fault current to the utility's transformer over their neutral.

What about transformers? Well, the ground /neutral bond you make at your first overcurrent device after the transformer performs the same function for any 'lost' transformer secondary current.

Yet, the all of your services need to also be tied into the building's ground system. This system- the Ufer, ground rod, whatever - is best thought of as being there for lightning, though that's a bit overly simplified. What matters is that you don't want one end of the building to be at a different ground potential than the other end.

We keep this from happening by tying all our ground rods, Ufers, etc., together. If you do not have serious building steel - not even bar joists holding up the roof or a concrete slab - then you're stuck with running a ground wire back all the way to the existing ground rods.

If you want to look just like the handbook, connect a 250.66 sized jumper from each transformer to the 2/0 grounding electrode conductor and connect them with split bolts.

The 5 kva control transformer is being fed from the mcc panel with two #12 and a ground on a 10 amp fuse, its leaving the mcc with grounding type sealtight, and returning to the mcc with the same type sealtight supping one 20 amp fuse to fed the computer,and one 20 amp fuse for printers. Do I still need grounding bushing if so what size wire, and do I need a ground back from xo to the main ground bar in the mcc, bonding xo in the transformer with #8. Also the main bonding will be done on a 2"x1/4 buss bar, can the buss be mounted with spacers on 3/4 plywood.

What is the smallest neutral I can use on this service, no 277 volt load just useing the neutral up to the first disconnect.

Can't be smaller than the required GEC...

The 5 kva control transformer is being fed from the mcc panel with two #12 and a ground on a 10 amp fuse, its leaving the mcc with grounding type sealtight, and returning to the mcc with the same type sealtight supplying one 20 amp fuse to fed the computer,and one 20 amp fuse for printers. Do I still need grounding bushing if so what size wire, and do I need a ground back from xo to the main ground bar in the mcc that is grounded back to the main panel, bonding xo in the transformer with #8 back to the gec.

Isn't an exothermic weld or a non-reversible crimp required instead of split bolts?

250.30(A)(4)(c) says