main bonding jumper connection schemes

[buffnitup]

Ok everyone I have a few questions. Here is an example and its setup.

200A Load Center in a Manufactured Home
200A disconnecting means outside on pole(required by utility company)

Ok now correct me if I am wrong. Since the disconnect is outside... the grounded conductor and equipment grounding conductor(s) shall be bonded by a main bonding jumper which in this case could be a #4 AWG Cu wire NEC 250.28(D)(1)----> (Table 250.66) from the ground bar in the inside load center to the neutral bar in the outside disconnect. I guess another option could be to use an EGC sized by 250.122 #6 AWG Cu run it from inside ground bar to outside ground bar then make main bond in outside enclosure either by screw already provided or the previous sized #4 between the ground and neutral bars. The latter would probably save on wire cost. Remove main bonding jumper in inside load center. Then the load center is no longer your service disconnecting means. May depend on AHJ how to do it.

Someone please elaborate the equipment bonding jumper. Is this mainly aimed at electrically connecting any non current carrying equipment such as load centers, conduit, subpanels, metal boxes together via bonding locknuts, wire, etc.?

What is the most economical disconnecting means outside? Safety switches are expensive as load centers. Would like something simple and small but if a big enclosure is cheaper then I guess it's better to go with that. Any suggestions?

 

[LarryFine]

The MBJ is the connection in the pole-mounted disconnect that joins the utility and feeder neutrals to the house feeder's EGC, the enclosure, and any electrode conductors. When only one busbar is used for both neutrals and EGC's, such as in a main-breaker panel, the bonding screw merely bonds the enclosure to it.

The house's panel is wired like any sub-panel as far as separate neutrals and EGC's, with the enclosure bonded to the EGC's, and not the neutrals. Two differences, though: as a separate structure, the house panel needs a main disco, and it needs an EGC system, the latter of which is usually the main's electrode system.

Added: Oh, and welcome to the forum!

 

[mcclary's electrical]

What code cyclye are you under? How many wire are going from the service disconnect to the panel inside?

 

[jxofaltrds]

Disconnect on the pole should have a bonding screw. No jumpers needed.

4 wire to the HUD unit per article 550.

The 'home' will already be set up for a 4 wire system.

'Sounds' like you want to run a 3 wire system from the disconnect to the home. Not allowed under 2008 NEC.

Read article 550.32. This may help your installation in under the 2005 NEC or later. If you are going from the pole to the disconnect required in 550.32.

If you are on a permanent foundation you can mount the disconnect on the home.

 

[buffnitup]

Thanks for your inputs. I went to electrician school for 2 years. Alot of book work but not much hands on. jxofaltrds when you speak of 4 wire. That's 2 ungrounded, 1 neutral, and an EGC I'm assuming. Do you speak of 550.33 Feeders?

 

[Dennis Alwon]

Thanks for your inputs. I went to electrician school for 2 years. Alot of book work but not much hands on. jxofaltrds when you speak of 4 wire. That's 2 ungrounded, 1 neutral, and an EGC I'm assuming. Do you speak of 550.33 Feeders?

Yes, he is speaking of 2 hots, neutral and an egc per 250.32(B) for a separate structure. The home is considered a separate structure from the pole, IMO.

It also looks like 550.33 requires it.

 

[jxofaltrds]

Yes, he is speaking of 2 hots, neutral and an egc per 250.32(B) for a separate structure. The home is considered a separate structure from the pole, IMO.

It also looks like 550.33 requires it.

Correct. If the pole is within the 30' and in sight then use 4 wire to the home. If the pole is over 30' or not in sight then another disconnect is required.

If 2005 NEC or older then you could use 3 wire between the two disconnects.

 

[buffnitup]

Ok. Too many rules lol So what you guys are saying if the disconnect is mounted in or on the home then this voids the "separate structure " rule. I never really knew thats what they meant. I figured since it's feeding the home its considered a part of that structure. I haven't looked but does this apply to a normal residence on a slab? I guess so according 250.32(B)

What's the least expensive means of an outside disconnect? With all AHJ rules aside.

 

[Dennis Alwon]

Correct. If the pole is within the 30' and in sight then use 4 wire to the home. If the pole is over 30' or not in sight then another disconnect is required.

If 2005 NEC or older then you could use 3 wire between the two disconnects.

Could you tell me where this 30 feet comes from?

 

[Dennis Alwon]

Ok. Too many rules lol So what you guys are saying if the disconnect is mounted in or on the home then this voids the "separate structure " rule. I never really knew thats what they meant. I figured since it's feeding the home its considered a part of that structure. I haven't looked but does this apply to a normal residence on a slab? I guess so according 250.32(B)

What's the least expensive means of an outside disconnect? With all AHJ rules aside.

I am not following you. Many believe that a pole is a separate structure. If the service is mounted on the main building, then any feeds from that panel to any building that is not attached to the building with the service is a separate structure.

If a building has a roof between the separate structures then they may be considered one building.

 

[buffnitup]

Not trying to confuse but I'm talking about a 4" X 6" pole within 30' with a disconnect 200A. Now it will only be feeding the home. No other building. What is confusing me is the separate structure thing. I have always thought it meant like a shed, barn, etc. Article 215.6 does require an EGC be run with feeders supplying branch circuits that require EGCs. If my understanding is right a feeder is any conductor between the disconnect and the FINAL ocpd. which in this case would be the conductors from the load side of the disconnect to the main breaker inside the load center.

 

[Dennis Alwon]

Not trying to confuse but I'm talking about a 4" X 6" pole within 30' with a disconnect 200A. Now it will only be feeding the home. No other building. What is confusing me is the separate structure thing. I have always thought it meant like a shed, barn, etc. Article 215.6 does require an EGC be run with feeders supplying branch circuits that require EGCs. If my understanding is right a feeder is any conductor between the disconnect and the FINAL ocpd. which in this case would be the conductors from the load side of the disconnect to the main breaker inside the load center.

If you look at the definition of structure it states

Structure. That which is built or constructed.

Vague- perhaps but I take that a 4x4 to be a structure. I will tell you that there are some inspectors in this area do not see the post as a structure.

I still do not know where the 30' comes into play. The statement below just means that the service equipment must be within 30' to count. It does not mean the pole is not a separate structure.

550.32 Service Equipment.
(A) Mobile Home Service Equipment. The mobile home service equipment shall be located adjacent to the mobile home and not mounted in or on the mobile home. The service equipment shall be located in sight from and not more than 9.0 m (30 ft) from the exterior wall of the mobile home it serves. The service equipment shall be permitted to be located elsewhere on the premises, provided that a disconnecting means suitable for use as service equipment is located within sight from and not more than 9.0 m (30 ft) from the exterior wall of the mobile home it serves and is rated not less than that required for service equipment per 550.32(C). Grounding at the disconnecting means shall be in accordance with 250.32.

 

[jxofaltrds]

Could you tell me where this 30 feet comes from?

Dennis

550.32.

 

[Dennis Alwon]

Dennis

550.32.

Since you posted when I did you may have missed my post. Read the one just before yours.

 

[jxofaltrds]

Dennis

We agree that the pole is a seperate structure.

 

[buffnitup]

I do see how it can be separate. Maybe they should change this in the code book. Maybe it should say if the means of support of the service equipment is separate from one or more buildings or structures being served... Maybe it does. Not making an argument just they should clarify somewhat. It is a manufactured home so 550.32(B) applies but I think in 550.32(B)(7) if the Svc Eqp is not installed on or in the manufactured home then other provisions, which I guess is 550.32(A), would apply. Which throws us to 250.32. You guys are right but like you say vague. In 550.32(A) it does say not to be mounted on or in the home. In 250.32(B) it indirectly calls the home a separate location supplied by a feeder from the service equipment located "away,off, not in" the home.

 

[Dennis Alwon]

I do see how it can be separate. Maybe they should change this in the code book. Maybe it should say if the means of support of the service equipment is separate from one or more buildings or structures being served... Maybe it does. Not making an argument just they should clarify somewhat. It is a manufactured home so 550.32(B) applies but I think in 550.32(B)(7) if the Svc Eqp is not installed on or in the manufactured home then other provisions, which I guess is 550.32(A), would apply. Which throws us to 250.32. You guys are right but like you say vague. In 550.32(A) it does say not to be mounted on or in the home. In 250.32(B) it indirectly calls the home a separate location supplied by a feeder from the service equipment located "away,off, not in" the home.

Either way it will still require 4 wires to the mobile home and a main breaker is required inside the home. The only difference is whether or not two ground rods are necessary at both locations. I don't believe art.550 requires that anyway. I am at the beach without code book so I did not check.

 

[LarryFine]

The only difference is whether or not two ground rods are necessary at both locations.

They are, but the same electrodes can be used for both structures (which is another reason a 4-wire feeder is a must.)

 

[buffnitup]

Yes the whole point of the EGC is understood. I believe 250.32(B) takes care of the grounding and grounding electrode installation. It says for a grounded ac system located at the separate structure install an egc with the supply conductors to the disconnecting mean and grounding electrode. It shall be used for grounding and bonding of the equipment. Thank you all for helping me understand some of this.

 

[jxofaltrds]

I do see how it can be separate. Maybe they should change this in the code book. Maybe it should say if the means of support of the service equipment is separate from one or more buildings or structures being served... Maybe it does. Not making an argument just they should clarify somewhat. It is a manufactured home so 550.32(B) applies but I think in 550.32(B)(7) if the Svc Eqp is not installed on or in the manufactured home then other provisions, which I guess is 550.32(A), would apply. Which throws us to 250.32. You guys are right but like you say vague. In 550.32(A) it does say not to be mounted on or in the home. In 250.32(B) it indirectly calls the home a separate location supplied by a feeder from the service equipment located "away,off, not in" the home.

My words:

(F) says no lower than 2' above grade.

(A) If not on a foundation.

Tell us how you want to install it and which NEC you are under, then we can say yes or no.