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View Full Version : What is the difference between a sub-panel and a panelboard (distribution panel)?



plazawest
Mar 27, 2010, 08:14 AM
I have a 200 amp meter/main installed on the outside of my home. I want to install a 100 amp "not sure what you call it" on the outside of the house also. I need to know:

1. What is the correct name of this?
2. Do I separate the neutrals and the grounds?
3. Do I need 3 conductors and a ground or 2 consuctors and ground?

Thanks,

A J

manhattan42
Mar 27, 2010, 08:29 AM
1. Any panel is a 'panelboard' or a 'distribution panel'. A main panel is a panelboard. A subpanel is a panelboard. A main is a 'distribution panel'. A subpanel is a 'distribution panel'.

These are sometimes separately described as 'main distribution panel' or 'sub (distribution) panel' just for clarity sake.

2. Not exactly sure what you are asking when you say: "Do I separate the neutrals and the grounds." Neutrals and grounds should never be placed under the same shared lugs in any panel.
Neutrals and grounds are typically connected to lugs in their respective neutral buss or ground buss although depending on the panel, there may only be 1 single buss for both neutrals and grounds.

3. For feeders to sub-panels, you must run a 3-wire conductor, which has 2 'hots', 1 neutral and 1ground... and the sub-panel itself should not be bonded with a bonding screw.

plazawest
Mar 27, 2010, 08:56 AM
Thanks for your response Manhatten42---

I sometimes install a 400 amp meter/main that has (2) 200 amp main brakers inside. One feeds the panel itself and the other will go to another ""panel" somewhere in the house. Is this any different then having a meter/main combination and feeding a panel inside the house from a "branch circuit", say a 100 amp? Are both of these called the same thing? Do both have the same bonding requirements?

Is there ever a case where you bond a "secondary" panel located down from the main panel?


Thnaks,

A J

manhattan42
Mar 27, 2010, 09:22 AM
Thanks for your response Manhatten42---

I sometimes install a 400 amp meter/main that has (2) 200 amp main brakers inside. One feeds the panel itself and the other will go to another ""panel" somewhere in the house. Is this any different then having a meter/main combination and feeding a panel inside the house from a "branch circuit", say a 100 amp? Are both of these called the same thing? Do both have the same bonding requirements?

Is there ever a case where you bond a "secondary" panel located down from the main panel?


Thnaks,

A J

Depends.

In some 400amp service configurations, the 400amp meter bases also contain a main 400amp disconnect. In such cases there are usually 2 200amp panels located in the house and both are 'subpanels'. The conductors from the meterbase/main disconnect in this case are 'feeders', and each 200amp panel does not get bonded. (This would apply also if you had 2 200amp main disconnects in a 400amp meter/main combination piece of equipment as you describe.)

Other times, a 400amp meter base has no main disconnect at all, so each separate 200amp panel located in a house is now a separate 'main', the conductors cables from the meter base are 'service entrance cables', and each panel will need to be separately bonded.

You need to determine if your 'subpanels' are really subpanels or if they are 'mains'.

Mains get bonded, subpanels do not.

Subpanels get bonded back to the main by way of the feeder equipment grounding conductor...

stanfortyman
Mar 27, 2010, 10:58 AM
This should have been kept in the same thread.
Please do not start a new thread to continue a conversation.

http://www.askmehelpdesk.com/electrical-lighting/what-difference-between-sub-panel-panelboard-distribution-panel-460700.html

donf
Mar 27, 2010, 11:42 AM
A Main Service Panel is fed directly from the Power Company. The incoming cable from the power company contains 2 Ungrounded conductors ( also known as Hots and one Neutral which is a grounded conductor)

The two hots each connect to their own breaker. Neutral connects to the Neutral bus. As a voltage test, With a Volt Meter you should at least 240 VAC with a probe on each of the hot conductors. There should also be 120 VAC between each Hot and Neutral.

The Residential Main Service panel has two phase bars. These are connected to each of the Hot conductors after the power is fed through the breaker.

Within the Main Service Panel, there are also one or more "Neutral Bus Bars" and one or more "Ground Bus Bars".

In the Main Service Panel and ONLY IN THE MAIN SERVICE PANEL, the Neutral and Ground are "Bonded" together. (Physically connected together). The EGC, equipment grounding conductor connects the panel Ground to the Earth Ground (Rebar in the concrete (2008 NEC Code) and one or two grounding rods (placed at least 6 feet apart) and/or within 5' of the cold water metal pipe feeding the house. (Note, there must be at least 10' of metal water pipe leading away form the house)

A sub panel however is fed off the main panel, from either Pass through lugs or a double pole double throw breaker (for 240 VAC). It must be a 4 wire connection. Black - Red (Phases) - White (Neutral) and an Insulated Green. If you are planning on six or less breakers, you can use a MLO sub panel with six breakers that can each be opened in an emergency. Any more then six breakers, and you need to either feed a main cutoff switch prior to entering the sub panel or a MB style cabinet sub panel.

The arrangement of connections is very similar to the main panel. If the sub panel is connected to the same building as the main, then you can connect the sub panel to the main panel's grounding system. NEUTRAL AND GROUND CANNOT BE BONDED TOGETHER IN ANY SUB PANEL.

If the sub panel is for use in a separate building, a detached garage for example, then the main panel must feed the sub panel inside the second structure. If the location is a remote structure, then you must sink one and possibly two ground rods and ground the sub panel to these rods.

As kind as a foot note, if this is going to be used in a remote structure then you must provide a circuit for an entry way light above the entry door.

tkrussell
Mar 28, 2010, 04:35 AM
There is no such thing as a Main Panel or a Subpanel, in the true technical context of electrical distribution.

The issue begins at the Main Service Disconnecting Means, AKA Main Circuit Breaker.

It is only at the MCB that the neutral is grounded to earth via a grounding electrode, either metal water main or ground rods, AND is the only location on the load side of the Main that the neutral and grounding is connected.

IF the first, or only panel, contains the MCB, the neutral and ground is connected and grounded. This is often called the Main Panel.

However, often I can have the MCB out at the meter, the only panel inside can be called the Main Panel, and other panels can be fed by it, and call those subpanels, but the wiring method is different when the Main Breaker is remote, not in that Main Panel.

Since only at the Main Service Disconnecting Means can the neutral and ground be connected and grounded, from that point on, to the "Main" panel or to any other panel, there shall be 4 wires, with separate neutral and grounding conductor, and at any of these panels the neutral must be insulated and isolated from any grounding conductors.


So. Plaza, to answer your questions, the new 100 amp panel must have a 4 wire feeder from the 100 amp breaker to be installed in your "Main" panel, and the neutrals and grounds must be separated at the new panel, and the neutral bar must not be bonded,(connected) to the equipment ground.

manhattan42
Mar 28, 2010, 05:04 AM
"It is only at the MCB that the neutral is grounded to earth via a grounding electrode, either metal water main or ground rods, AND is the only location on the load side of the Main that the neutral and grounding is connected."

Actually, this above isn't true.

250.24(A)(1) of the NEC says:

"The grounding electrode conductor connection shall be made at any accessible point from the load end of the service drop or service lateral to and including the terminal or bus to which the grounded service conductor is connected at the service disconnecting means."

The grounding electrode conductor can be connected to the meter base if allowed by the utility.

It can even be connected to the CT cabinet.

It can even be connected to a wireway that distributes conductors to multiple MCBs..

Most commonly it is done as tkrussell states, but it does not have to be.

tkrussell
Mar 28, 2010, 05:09 AM
Manhattan, I stated, " on the load side of the Service Disconnecting Means.

After grounding the neutral at the main, the neutral and equipment ground SHALL NOT be connected.


Grounding an be done at the meter and at the transformer, as these locations are on the Line side of the Service Disconnecting Means.

A CT Cabinet will need to be or at the Service Disconcerting Means, but cannot be at both.

Connecting "to" a wireway is not allowed. If you meant a wireway containing the main system neutral lug for the service, and this neutral is for multiple circuit breakers, no more than six are allowed to act as the Service Disconnecting Means, then fine.


So what did I say that is not true?

Please explain exactly where grounding of the neutral and connection to equipment ground can be done besides at the Service Disconnecting Means?

manhattan42
Mar 28, 2010, 08:38 AM
Thanks for the clarification regarding the "on the load side of the service disconnecting means."

I misread your remarks as "load side of the service" and apologize for the error.

However, "The issue begins at the Main Service Disconnecting Means, AKA Main Circuit Breaker" is not necessarily true.

The Main Service Disconnect and the Main Circuit Break are not the same thing and are not necessarily in the same location.

They can be the same and in the same location, but do not have to be nor always have to be.

They main disconnect does not necessarily even have to be 1 MCB. It can be up to 6 MCBs... further complicating the matter.

You can have a single service with several mains... as is the case of multi-occupancy apartment buildings or multi-occupancy tenant spaces.

In such cases, the grounding electrode conductor can be located at a 'tap box' after the service drop or at each individual tenant 'main'.

And again, it is permissible to locate the electrode grounding conductor at a CT cabinet or a wireway from which multiple main dristribution panels are run provided each is located between the service drop and the bus where the grounded service conductor is connected at the service disconnecting means.

250.24(A)(1) absolutely permits it.

All this is slightly off topic to the original question at hand, but is relevant since determining when a panel is a 'main' or a 'subpanel' may not be that easy given all the nuances the Code allows.

No disrespect meant or intended, and I appreciate your clarifications and corrections (of me).

Regards

tkrussell
Mar 28, 2010, 10:36 AM
You cite very specific installations, that under certain, advanced circumstances are different, and can be other points to ground the neutral.

For the purpose of residential DIY'ers, only ground the neutral at the enclosure that contains the Service Disconnecting Means, AKA Main Breaker.