Mike01 said:
That is correct for the equipment bonding jumper, however on a SDS if the connection is made at the source (step down xfmr) looking at exhibit 250.13 in the 2008NEC Handbook, this indicates the equipment bonding jumper is the connection between the XO and the case, however the connection from the XO to the ground bar in the downstream device (panel, c.b. etc.) is indicated as the system bonding jumper and according to 250.30 grounding separately derived alternating-current systems 250.30(1) system bonding jumper is sized based on the derived phase conductors and does not mention 250.102( C) until 250.30(2) wich indicated the equipment bonding jumper size where the wire type is run with the derived phase conductors form the source of the SDS to the first disconnecting means. So does this mean that the largest size system bonding jumper (when the equipment bonding jumper is installed at the SDS xfmr) that the largest system bonding jumper required is a 3/0 in each conduit?
"system bonding jumper required is a 3/0 in each conduit?"
System bonding jumper in a conduit ? . No such thing exists !
If it's in the conduit, it's either an Equipment bonding jumper or an Equipment grounding conductor depending on if it's line or load to the neutral ground/bond point. . Let me explain using exhibit 250.13.
I got another look at exhibit 250.13 and it is unquestionably screwed up !
Equipment Grounding Conductors, Equipment Bonding Jumpers, Main Bonding Jumpers, and System Bonding Jumpers are all closely
related but are not the same thing nor are they covered by the same sections in 250.
The starting point would be to determine where exactly the
neutral is grounded/bonded in the system. . If it's the service, it will be grounded/bonded by the utility at poles and transformers and even possibly the meterbase, but none of that counts. . The neutral ground/bond to the electrode(s) and the main disconnect enclosure is the
Main Bonding Jumper, 250.24(B).
For a separately derived system, you will have a neutral ground/bond to at least one electrode
and either the transformer enclosure
or the first disconnect enclosure [for an
outdoor transformer, you're allowed to do both, 250.24(A)(2) unless this causes the type of issue raised in 250.6(B)]. . In exhibit 250.13 I clearly see this jumper from neutral to building steel electrode and enclosure at the transformer and it's
incorrectly labeled "Equipment bonding jumper". . . The neutral ground/bond to the electrode(s) and the transformer or first disconnect enclosure is the
System Bonding Jumper, 250.30(A)(1).
Any grounding bar bond to any enclosure with the neutral bar
isolated from the enclosure [and all other grounds] is an
Equipment Bonding Jumper. . They don't bother labeling that at all in the first disconnect in exhibit 250.13.
When you leave the enclosure that contains the system bonding jumper [which is depicted as the transformer], exhibit 250.13 shows an uninterrupted conductor to a load side enclosure and
incorrectly labels it "System bonding jumper". . An uninterrupted conductor from the system bonding jumper enclosure to another enclosure on the load side is an
Equipment Grounding Conductor. . For conduit serving as an equipment grounding conductor, a jumper across an expansion joint or from bonding locknut/bushing to enclosure would be called an
Equipment Bonding Jumper, 250.102.
The only time that the conductor running from transformer to first disconnect is called an equipment bonding jumper [rather than an equipment grounding conductor] is when the neutral ground/bond to the electrode(s) and enclosure is found at the first disconnect instead of at the transformer. . That conductor/jumper from enclosure to enclosure is on the
line/supply side of the enclosure that contains the system bonding jumper when the system bonding jumper is in the first disconnect, 250.30(A)(2).
That last paragraph sounded a little confusing when I read it back to myself so let me try to say it another way:
If you look at
2 different SDS examples and both have a grounding/bonding conductors/jumpers run with the other conductors. . What do you call this wire ?
Example #1 has the neutral grounded/bonded to the electrode(s) and the enclosure at the
transformer. . The grounding/bonding conductor/jumper from enclosure to enclosure is on the
load side of the neutral ground/bond point and is an
Equipment Grounding Conductor, 250.110.
Example #2 has the neutral grounded/bonded to the electrode(s) and the enclosure at the
first disconnect. . The grounding/bonding conductor/jumper from enclosure to enclosure is on the
line/supply side of the neutral bonding point and is an
Equipment Bonding Jumper, 250.30(A)(2).
The problem with exhibit 250.13 playing "loosey goosey" with these terms is that you have to go to a different code section depending on which wire you are dealing with.
Main Bonding Jumper, 250.24(B)
System Bonding Jumper, 250.30(A)(1)
Equipment Bonding Jumper, 250.102
Equipment Grounding Conductor, 250.110
Tell me if my explanation makes sense to you.
