Bonding screw in the distribution (sub) Panel

[al hildenbrand]

So what does a 3 phase have? 3 hots, neutral, and ground? Thank you for clarifying.

Exactly. Five wire.

 

[LRB]

3 PHASE, 4 OR 5 WIRE FEEDERS

3 PHASE, 4 OR 5 WIRE FEEDERS

Many industrial 3 phase feeders do not utilize a neutrial (grounded conductor), and are therefore 4 wire (conductor) circuits.If their are no phase to neutrial loads, the neutrial does not need to extend past the service disconnect,

 

[Strathead]

So from my prospective as a home inspector I am usually inspecting homes that are 10-20 years old and I see and point out that grounds and neutrals should be separated in the sub panel. How important (as a safety issue) should this be corrected. Had a building inspector tell me it is not required to correct unless they are adding/upgrading the sub panel.

A couple things. First here is a typical panel ground bar. Another post explained to you about insulated bars that have a green screw through them. As you can see this bar is bare so by its nature it will be in contact with the can. By code grounding wires, (the green or bare wires) have to be connected to all non current carrying metal parts of electrical components (within reason).

Second, the issue you cite here. What I have found is that many old houses were built with a meter outside and then the feeder extended well inside the house to the first means of disconnect usually a panel with the neutrals and the grounds bonded at that point. Later some person installs a disconnect outside but no one is astute enough to know that they have to replace the feeder and separate them. In this area I have seen less reputable (IMO) electrical contractors quote cheap sight unseen knowing that it is typical in this area, and then offer a huge upcharge to fix the problem once they start the work.

 

[al hildenbrand]

Many industrial 3 phase feeders do not utilize a neutrial (grounded conductor), and are therefore 4 wire (conductor) circuits.If their are no phase to neutrial loads, the neutrial does not need to extend past the service disconnect,

Yes, but this thread is about a home inspector's questions about common dwellings, just saying. . . and the means of bonding the panel enclosure to the equipment grounding conductor via terminal bars.

 

[kwired]

Many industrial 3 phase feeders do not utilize a neutrial (grounded conductor), and are therefore 4 wire (conductor) circuits.If their are no phase to neutrial loads, the neutrial does not need to extend past the service disconnect,

OP is a HI and probably almost never sees 3 phase installations.

But we can throw in even more confusion with 3 phase 3 wire applications:happyyes:

 

[LRB]

three phase question

three phase question

Al and Kwired, you are absolutly correct, however the OP opened this can of worms in thread 19, asking about three phase systems, therefore I was responding to the OP question in thread 19.

 

[al hildenbrand]

What I have found is that many old houses were built with a meter outside and then the feeder extended well inside the house to the first means of disconnect usually a panel with the neutrals and the grounds bonded at that point. Later some person installs a disconnect outside but no one is astute enough to know that they have to replace the feeder and separate them. In this area I have seen less reputable (IMO) electrical contractors quote cheap sight unseen knowing that it is typical in this area, and then offer a huge upcharge to fix the problem once they start the work.

Strathead, this, in my opinion, is part of the core of what the home inspector is trying to understand, so, please pardon my nitpicking terms here.

The wiring between the electric meter and the "first means of disconnect," the Service Disconnect, is not a "feeder", but, rather, is still the service conductors, as there is no separate neutral conductor and equipment grounding conductor, but there is only a "grounded service conductor".

A "feeder" is the wiring between the Service Equipment and the final overcurrent protective device (most commonly fuse or circuit breaker). The Service Equipment houses the Service Disconnecting Means, the Main Bonding Jumper (that bonds the feeder neutral and equipment bonding conductor together to the Grounded Service Conductor) and it houses circuit breakers or fuses.

A feeder neutral carries current normally, and, in order to not leak current, is an insulated conductive path all the way back to the Service Equipment.

The subpanel metal enclosure does not "normally" carry any current. However it is connected (bonded) to the Equipment Grounding Conductor in order to create an effective fault clearing conductive path in the event of a live conductor shorting to the metal enclosure.

This is the answer to the heart of the OP home inspector's question, in my opinion.

 

[Strathead]

Strathead, this, in my opinion, is part of the core of what the home inspector is trying to understand, so, please pardon my nitpicking terms here.

The wiring between the electric meter and the "first means of disconnect," the Service Disconnect, is not a "feeder", but, rather, is still the service conductors, as there is no separate neutral conductor and equipment grounding conductor, but there is only a "grounded service conductor".

A "feeder" is the wiring between the Service Equipment and the final overcurrent protective device (most commonly fuse or circuit breaker). The Service Equipment houses the Service Disconnecting Means, the Main Bonding Jumper (that bonds the feeder neutral and equipment bonding conductor together to the Grounded Service Conductor) and it houses circuit breakers or fuses.

A feeder neutral carries current normally, and, in order to not leak current, is an insulated conductive path all the way back to the Service Equipment.

The subpanel metal enclosure does not "normally" carry any current. However it is connected (bonded) to the Equipment Grounding Conductor in order to create an effective fault clearing conductive path in the event of a live conductor shorting to the metal enclosure.

This is the answer to the heart of the OP home inspector's question, in my opinion.

I have no problem with you clarifying. Terms are important to the code. So if you are going to correct me isn't it actually "service entrance conductors"?

Seriously though, I feel this is partly at the core of what the HI needs to know anyway, so if he is reading this and it doesn't makes sense please ask for clarification.

 

[al hildenbrand]

. . . isn't it actually "service entrance conductors"?

An interesting point. I deliberately chose "Service Conductors" as the Article 100 Definition I wanted to use because it side steps the Overhead / Underground parts of those other two definitions for Service-Entrance Conductors.

Service Conductors. The conductors from the service point to the service disconnecting means.

Concise and to the point in this discussion, in my opinion.

 

[Unbridled]

I am a home inspector trying to understand what is correct and why in the distribution (sub) panel. My understanding is that beyond the service disconnect point (main panel) (in what I call the sub panel, I believe is called a distribution panel by NEC) ground (bare copper wire) and neutral (white wire) is separated and not bonded. My question is then is the ground bus bar bonded to the panel it self with the green screw? I have asked building inspector locally and electricians locally and I can not seem to get a clear understanding. So, hopefully someone can lay this out in laymen terms so I can be a better inspector. Thank you in advance.

Pretty Simple.
Simply Float the Neutral Terminal Bar (No contact with panel enclosure) in your sub-panel AND install a grounding terminal bar directly to the sub-panel enclosure which will now bond the enclosure. There is nothing wrong with installing the green screw into the ground bar, but it's not necessary if the bar ground bar is already screwed to the sub-panel frame.

 

[donhawley]

I am a different HI and have a very specific question on bonding remote panels. If a remote panel has a three wire feed HHN and no ground or metallic conduit connection to the service panel, is it correct to have the branch wiring grounds and neutrals on the isolated neutral bus? If not where would the ground wires on a separate ground bar be connected to the rest of the circuit? Everyone hear keeps speaking of 4 wire feeds to remote panels and we see way more three wire feeds than 4 wire even though they are no longer allowed.

 

[al hildenbrand]

I am a different HI and have a very specific question on bonding remote panels. If a remote panel has a three wire feed HHN and no ground or metallic conduit connection to the service panel, is it correct to have the branch wiring grounds and neutrals on the isolated neutral bus? If not where would the ground wires on a separate ground bar be connected to the rest of the circuit? Everyone hear keeps speaking of 4 wire feeds to remote panels and we see way more three wire feeds than 4 wire even though they are no longer allowed.

The separation of neutrals and grounds in subpanels (remote panels) is an old requirement, at least half a century (without doing the research for the exact amount more than half a century). That means you are probably looking at old fuse centers that had the neutral bus riveted to the enclosure. If you are seeing this in circuit breaker panels, that is a problem that should be evaluated by a professional.

For that matter, because of the complexity of the changes in the requirements over the last 75 years, it is best to have it professionally evaluated.

Having over half of the subpanels that you encounter in your inspections being three-wire ungrounded is really rather alarming. Perhaps there are local historical ordinances or AHJ interpretations that have resulted in such a large count.

 

[kwired]

I am a different HI and have a very specific question on bonding remote panels. If a remote panel has a three wire feed HHN and no ground or metallic conduit connection to the service panel, is it correct to have the branch wiring grounds and neutrals on the isolated neutral bus? If not where would the ground wires on a separate ground bar be connected to the rest of the circuit? Everyone hear keeps speaking of 4 wire feeds to remote panels and we see way more three wire feeds than 4 wire even though they are no longer allowed.

I have to say I'd rather see them land the EGC's on the neutral/install the bond screw then to leave the EGC's "floating". It should still be included as a violation in your report though. Now if the panel in question is in a separate structure - that was allowed and existing installations are still allowed to remain that way, with some conditions.

 

[FionaZuppa]

if you feed a sub panel via a gfi ocpd from main, you cannot have egc land on N bar in sub panel, thus making a 3 wire sub panel (i assume 240vac L-N-L) to need a isolated N bar, thus to have a earthed sub panel you need a 4 wire feeder. why would anyone not install a 4 wire feeder for 240vac sub panel?

where in NEC code is it a violation to terminate feeder egc to the frame of sub panel (using correct terminations) ? just asking.

 

[david]

i think it needs clarified for home inspectors that the sub feed panels being discussed here involving four conductors are within the same structure.

If the panel being sub-feed with three conductors is with- in a separate structure this becomes a different discussion

I would hate to see home inspectors start writing up all three conductor sub-feeds they come across

Unless you're dealing with a separate structure and prior to the 2008 NEC you will almost always need a "4 wire" feeder. IMO there wouldn't have been a code change in 2008 if the CMP felt that a 3-wire feeder were just as safe as a 4-wire feeder.

 

[Smart $]

So what does a 3 phase have? 3 hots, neutral, and ground? Thank you for clarifying.

It appears this thread is going walkabout.

Technically systems should never be referred to with the grounding wire being a system wire. Ground wires should be referred to separately on feeder or cable schedules, and any discussion thereabout.

Most homes in the USA are 120/240V 1Ø 3W. This is a single phase (1Ø) system with two ungrounded and one grounded neutral 'wire' (3W). Per Code it is required to be a grounded neutral system.

If a home is three phase it will likely be 208/120V 3Ø 4W or 240/120V 3Ø 4W (aka high leg delta). As you can see by the nomenclature, both are a 4-wire system... with ground (EGC) after the service disconnecting means.

 

[kwired]

why would anyone not install a 4 wire feeder for 240vac sub panel?

where in NEC code is it a violation to terminate feeder egc to the frame of sub panel (using correct terminations) ? just asking.

first question - I run into a lot of older installs where the installer was either not qualified at all or was not up to speed on why they shouldn't do it that way, OP is a home inspector and you kind of have to think whenever he runs into that it is for similar reasons, he knew it wasn't right but was asking why it isn't right.

second question - you shouldn't find anything that prohibits what you asked about (assuming correct termination methods, coarse thread self tapping screw, not scraping paint are no-go's but because of termination method not because you can't land an EGC on the frame of the cabinet.

 

[FionaZuppa]

first question - I run into a lot of older installs where the installer was either not qualified at all or was not up to speed on why they shouldn't do it that way, OP is a home inspector and you kind of have to think whenever he runs into that it is for similar reasons, he knew it wasn't right but was asking why it isn't right.

but if the sub has all gfi ocpd's then running 3-wire (L-N-L) feeder is bad?

 

[kwired]

but if the sub has all gfi ocpd's then running 3-wire (L-N-L) feeder is bad?

Depends on what you want to call "bad". Any alternate paths for neutral current to flow will trip the GFCI when such current exceeds 4-6 mA. That is good in that it reduces risk of shock, bad in that it creates a lot of functionality issues.

 

[FionaZuppa]

Depends on what you want to call "bad". Any alternate paths for neutral current to flow will trip the GFCI when such current exceeds 4-6 mA. That is good in that it reduces risk of shock, bad in that it creates a lot of functionality issues.

i mean in context of the HI. in this case a L-N-L feeder to a sub is nothing to worry about if the sub branch ckt's have full gfi coverage via ocpd or 1st gfi device?