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Subject - SIZING OF (G,E,C) FOR 320A SERVICE
ikayla Hello all. Pardon my ignorance but can someone please help me to understand article 250.66.
1:i installed a 400A service with two panels.from the meter base to panel(s) i used two 4/0 AU SE cable.what size G,E,C should be used for bonding of the water system?

2:do i have to bond to well case 600'down? (there is two G,E @ 6 FEET apart) from well to dwelling water supply is nonmatalic (plastic-PVC)

3:should i bond to steel beams? measured between steel beam and phase got 118V.

4:is the equptment ground suffient for bonding of furnace?

thanks for the help hope to hear from the board soon
kbsparky 250.66 can be confusing, to say the least. Since you have installed parallel service conductors, you have to add their cross-sections together to determine the minimum size of grounding electrode conductor.

A 4/0 is slightly smaller than 250 kcmil, so two of them will be less than 500 kcmil. Therefore, you have to use the size required from "over 250 through 500" which translates into a #2 copper GEC.

You could refer to table 8 which shows that a 4/0 = 211.6 kcmil and multiply that out, but I don't think it's worth the trouble, since the output range is quite wide, with any result between 250 and 500 kcmil requiring the same #2 GEC conductor

2) You only have to bond the well casing if it is metal, and it has 10 feet or more in direct contact with the earth, and your local inspector-critter requires it. You would be required to use that #2 GEC if this is the case. Some inspectors don't require this when the water supply is non-metallic.
See NEC 250.52(A)(1)

3) If you have building steel, it is also required to be grounded if it has an "earth" connection [See NEC 250.52(A)(2)] OR it is likely to become energized in a fault condition [see NEC 250.104(C)]. In either case that wire is to be sized according to 250.66.

4) Now this one is tricky. If the furnace is gas or oil, and has a metal piping system supplying it, the bonding jumper required needs to be sized to the largest branch circuit that passes that piping system. If the circuit supplying the unit has an equipment gounding conductor present that satisfies this requirement, then no additional bonding is required. You use table 250.122 to determine its size.
ikayla thanks kbsparky for your explanation very helpful (250.66).

did you mean [NEC 250.104(c)][structural metal]?
kbsparky
quote:
did you mean [NEC 250.104(c)][structural metal]?


Yes, you are correct. I have edited my earlier reply and fixed the error.
Electricman For this service? 250.66(A) since he is using 2 ground rods 6 feet apart is it permissible to use #6 for the EGC? Please explain if not. If that is so then the bonding conductor for the water pipe system would be larger than the service ground ? correct?
kbsparky Actually, the original poster of thie thread did not ask what size wire to use on the ground rods, he only stated they were installed.

You are correct, in that a made electrode (such as a ground rod) only needs a #6 wire, since that size is sufficient to carry all that a ground rod can protect.

AS for the other wires to water pipes, steel, etc. they are still required to be sized according to 250.66 or 250.122 as the case may be.
Electricman Ok, I was just making sure I was on the same page, One day I will get Article 250 down pat, Thanks
kbsparky
quote:
Ok, I was just making sure I was on the same page, One day I will get Article 250 down pat, Thanks


Let me know when that happens. I take a grounding and bonding continuing education course every few years, and I still have some problems with it. But those courses have helped my understanding considerably
Electricman Yeah Ken, I will let you know then you and I will write a book on it and make lots of $$$$$$$$$$$$$$, then no more attics for you and me
CTBigman 1:i installed a 400A service with two panels.from the meter base to panel(s) i used two 4/0 AU SE cable.what size G,E,C should be used for bonding of the water system? HMM I would say you only need a #4 CU Ground, if you used 2-4/0 SEU then you must have used 2-200A Main Breaker Panels, therefore IMHO you only have to size it for #4, your "main disconnect/service" is really only a 200A. does anyone disagree?? and if so why??
kbsparky
quote:
... does anyone disagree?? and if so why??...


I disagree, since your assumption violates the Code. Please read my earlier post in this thread, dated March 6, which includes the following text:
quote:
250.66 can be confusing, to say the least. Since you have installed parallel service conductors, you have to add their cross-sections together to determine the minimum size of grounding electrode conductor.

A 4/0 is slightly smaller than 250 kcmil, so two of them will be less than 500 kcmil. Therefore, you have to use the size required from "over 250 through 500" which translates into a #2 copper GEC.

You could refer to table 8 which shows that a 4/0 = 211.6 kcmil and multiply that out, but I don't think it's worth the trouble, since the output range is quite wide, with any result between 250 and 500 kcmil requiring the same #2 GEC conductor

Your Code reference here is Note 1 to table 250.66.

Unless you are under the exceptions provided by 250.66(A) through (C).
CTBigman Okay sparky define "parallel or multiple sets of conductors" it is my understanding that this is 2 separate 200A main breaker services. For example an 800A service fed with parallel 600MCM cables from a transformer to a dual lug 800A main breaker, these conductors would be parallel because they start and end together, that is how the 800A is provided. How can 2-200A main breaker panels be considered parallel feeders????
I try to write a trick code question and stick it in with each paycheck, it keeps my employees active in the code and they sometimes get into very heated discussions, which this subject happens to be this weeks question!!
lctrc789 Someone correct me if I am wrong, 250-66 is for the secondary side of the transformer grounding for instance you have a service with 4/0 feeders then you would have to have a grounding conductor the size of # 2 minimum. So if you have a 400 amp service and it is fed from say 500 kcmil conductors then you would need a 1/0 for grounding the water pipe,building steel etc...
Now the grounding conductor for the ground rod does not have to be larger then #6 wire.
250-122 is for grounding equipment raceways etc.. or what you would use on the primary side of a transfromer.
I would use the conductors that fed the 400 amp services toghether what ever size they were and then use 250-66 for grounded conductor then go to article 250-122 and see that I have a 400 amp service and would use minimum # 3 wire for equipment ground.(grounding conductor)
kbsparky
quote:
...it is my understanding that this is 2 separate 200A main breaker services....


Read the thread title again. This discussion is about a 320A SERVICE which was determined to be 80% (continuous) of a 400 Amp service drop. There was to be a single meter box, which then was fed into (2) 200 Amp panels for the branch circuits.

This is how we considered this parallel or multiple feeder conductors: They were paralleled in the main service drop or conduit, tied in together in the meter box, and only on the load side were split into loads for each panel.

Now, if you have separate meter boxes, one for each 200 Amp panel, then you are dealing with more than one service, and each service would have its GEC sized accordingly.

Make more sense now, or are we more confused
CTBigman Okay this should end the discussion, thanks sparky!