I'm looking for NEC article reference that will point me to the "25 ft. rule". I have a service that has a main disconnect. It feeds 3 panels. One less than 25ft. away and 2 that are greater than 25 ft. away. I was told that the 2 greater than 25 ft. away from the main disconnect will need to be MCB panels and the one less than 25ft. away will be fine as MLO. Thanks.
Panelboard MLO vs. MCB
- Thread starter new_ee
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kevinware
Senior Member
- Location
- Louisville, KY
Re: Panelboard MLO vs. MCB
How are the panels classified?? (Lighting and appliance, or Power Panel)
How are the panels classified?? (Lighting and appliance, or Power Panel)
- Location
- Lockport, IL
- Occupation
- Semi-Retired Electrical Engineer
Re: Panelboard MLO vs. MCB
240.21(B)(2)
240.21(B)(2)
Re: Panelboard MLO vs. MCB
Thanks. But I had it all wrong. There are separate meters for the 2 tenant panels that are more than 25 ft. away. Also there is no main disconnect. Each of the panels has a disconnect at the service entrance. The service entrance for all 3 panels is in the same location. So my question is are the panels still ok to be MLO? Even if the disconnect is more than 25 ft. from the panel? I think I explained this ok but if not let me know and I will try to explain it better.
Thanks. But I had it all wrong. There are separate meters for the 2 tenant panels that are more than 25 ft. away. Also there is no main disconnect. Each of the panels has a disconnect at the service entrance. The service entrance for all 3 panels is in the same location. So my question is are the panels still ok to be MLO? Even if the disconnect is more than 25 ft. from the panel? I think I explained this ok but if not let me know and I will try to explain it better.
- Location
- Lockport, IL
- Occupation
- Semi-Retired Electrical Engineer
Re: Panelboard MLO vs. MCB
There has to be some manner of overcurrent protection for the conductors that provide power to each of the three panels. If the "disconnect" you mentioned (all three of which are in the same area) has overcurrent protection (which I tend to doubt), then you can use a MLO panel, regardless of the distance. If it is just an on/off switch, then you need overcurrent protection somewhere.
240.21(B)(2) will tell you that you don't always have to have that overcurrent protection at the starting point of the conductors. You can add a breaker or fuse immediately downstream of the disconnect, and run a million miles of cable to an MLO. But if you don't have overcurrent protection there, then you must have it at the panel.
Being a "Lighting and Appliance Panel," as opposed to "Power Panel," is not relevant to your question.
There has to be some manner of overcurrent protection for the conductors that provide power to each of the three panels. If the "disconnect" you mentioned (all three of which are in the same area) has overcurrent protection (which I tend to doubt), then you can use a MLO panel, regardless of the distance. If it is just an on/off switch, then you need overcurrent protection somewhere.
240.21(B)(2) will tell you that you don't always have to have that overcurrent protection at the starting point of the conductors. You can add a breaker or fuse immediately downstream of the disconnect, and run a million miles of cable to an MLO. But if you don't have overcurrent protection there, then you must have it at the panel.
Being a "Lighting and Appliance Panel," as opposed to "Power Panel," is not relevant to your question.
kevinware
Senior Member
- Location
- Louisville, KY
Re: Panelboard MLO vs. MCB
Am I wrong for interpreting that with new_ee saying the panels are lighting and appliance panels. I go to 408.36(A) "Each lighting and app. branch circuit panelboard shall be individually protected on the supply side by not more then two main circuit breakers or two sets of fuses having a combined rating not greater than that of the panelboard." Is this not telling me that I need OCP at new_ee's panels?
And 408.36(A)Exception No.1 "Individual protection for a lighting and app. shall not be required if the panelboard feeder has overcurrent protection not greater than the rating of the panelboard." Isn't this telling me that I don't need an OCPD at new_ee's panels if the feeder from wen-ee's disconnect has an OCPD?
Just trying to see what I did wrong...
Am I wrong for interpreting that with new_ee saying the panels are lighting and appliance panels. I go to 408.36(A) "Each lighting and app. branch circuit panelboard shall be individually protected on the supply side by not more then two main circuit breakers or two sets of fuses having a combined rating not greater than that of the panelboard." Is this not telling me that I need OCP at new_ee's panels?
And 408.36(A)Exception No.1 "Individual protection for a lighting and app. shall not be required if the panelboard feeder has overcurrent protection not greater than the rating of the panelboard." Isn't this telling me that I don't need an OCPD at new_ee's panels if the feeder from wen-ee's disconnect has an OCPD?
Just trying to see what I did wrong...
- Location
- Lockport, IL
- Occupation
- Semi-Retired Electrical Engineer
Re: Panelboard MLO vs. MCB
You're not doing anything wrong. You did, however, provide the article that confirms my statement that if there is a OCPD at the origin of the feeder, then you don't need a main breaker at the panel. If you look at 408.36(B) (2005 version ?it was 408.16(B) in 2002), you will see that this is also true for a power panelboard. That is why I said the type of panel was not relevant to the question at hand.
You're not doing anything wrong. You did, however, provide the article that confirms my statement that if there is a OCPD at the origin of the feeder, then you don't need a main breaker at the panel. If you look at 408.36(B) (2005 version ?it was 408.16(B) in 2002), you will see that this is also true for a power panelboard. That is why I said the type of panel was not relevant to the question at hand.
Re: Panelboard MLO vs. MCB
Posted by kevinware:
New_ee: When you say "disconnect", I think everyone is taking that to mean a fusible disconnect or a circuit breaker or some type of OCP. (That's the most common type of disconnect for a service). Can we assume you meant a disconnect with OCP?
Posted by kevinware:
Nothing in that statement says the OCP has to be at the panel. It can be anywhere in the supply side.
New_ee: When you say "disconnect", I think everyone is taking that to mean a fusible disconnect or a circuit breaker or some type of OCP. (That's the most common type of disconnect for a service). Can we assume you meant a disconnect with OCP?
sceepe
Senior Member
Re: Panelboard MLO vs. MCB
Guy who taught me the business had a rule, install a MCP in the panel if the upstream disconnect (OCPD) is not in the same room as the panel in question. He did this not because he had to but because he thought it was the best way.
I agree. If you want to kill power to a panel, I don't want you to have to leave the electrical room to hunt the upstream disconnect.
Guy who taught me the business had a rule, install a MCP in the panel if the upstream disconnect (OCPD) is not in the same room as the panel in question. He did this not because he had to but because he thought it was the best way.
I agree. If you want to kill power to a panel, I don't want you to have to leave the electrical room to hunt the upstream disconnect.
- Location
- Massachusetts
Re: Panelboard MLO vs. MCB
If I go and shut it off at some other location once I verify it's dead I can forget about the PPE.
Everything is a trade off.
On the other side of the coin if I kill the panel with it's own MCB I still must wear PPE to service the panel.
If I go and shut it off at some other location once I verify it's dead I can forget about the PPE.
Everything is a trade off.
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