Subpanel safety theory

[Grey Eagle]

Theoretically, do you prefer a main lug or main circuit box. For example, a 100 amp box installed in a garage connected by #2 copper wire with a #6 ground run through inch and a quarter conduit.

 

[infinity]

Grey,

What kind of contractor are you?

 

[charlie b]

If I were to debate the virtues of MCB versus MLO, I would know that the cable and conduit sizes would not be part of the discussion.

I am putting a temporary hold on this thread. I am taking this action because I cannot tell from the member's profile whether he (or she) is employed in the electrical industry. The thread appears to me to be an attempt by a Do It Yourself person to obtain "how-to" information.

The Forum?s rules do not permitted us to provide ?how-to? assistance to a person who is not an electrician, but who appears to be planning to do electrical installation work at home.

I invite the Original Poster to send me a Private Message (click on my member name, and a pull down menu will appear), to explain the circumstances, and to let me know if I have misjudged the situation. If I have, I will reopen the thread, and post an apology for the delay and inconvenience.

 

[charlie b]

I received a PM from Grey Eagle. This is not a DIY situation, but rather an academic discussion amongst electricians in training. As promised, I hereby offer my apology for the delay and the inconvenience.

 

[charlie b]

Having reopened the thread, I'll now reopen the discussion. Could you please clarify your question? In what way does the cable size enter into your question? Are you asking what circumstances would suggest that an MCB panel would be best, and what circumstances would suggest that an MLO panel be best?

This really isn't a theory question, nor is it a safety question. The NEC allows the use of either, so long as everything is properly protected against overcurrent.

 

[dlhoule]

Theoretically, do you prefer a main lug or main circuit box. For example, a 100 amp box installed in a garage connected by #2 copper wire with a #6 ground run through inch and a quarter conduit.

What are you going to be supplying in this garage where you want a 100A panel? How far is garage from main panel?

Typically I prefer to have main breaker in panel. I like to be able to turn off the main and have the bus without power for changing or adding breakers.

 

[petersonra]

Theoretically, do you prefer a main lug or main circuit box. For example, a 100 amp box installed in a garage connected by #2 copper wire with a #6 ground run through inch and a quarter conduit.

The wire size is not an issue.

I personally don't like MLO PBs. But that is just personal preference. I like a way to shut off all the power on one throw.

 

[cpal]

Is the garage a seperat structure? If so how many circuits originate with in


Charlie

 

[Grey Eagle]

Subpanel question

Subpanel question

The cable size etc is not important. I was just trying to determine if there was a potential diffference in theory as far as safety between the two types.

I guess I need to get rich enough to get Mike's course on theory!

 

[George Stolz]

If you want the convenience of an extra handle to kill the panel you're about to work in, a MDP wouldn't be a bad idea. However, I think from a safety standpoint, the MDP is a bit misleading because the panel is still energized if you shut off that main breaker. So, PPE would still be required.

I use MLO's every day, and don't have a problem with it. There are specific times to use the different types, it just depends on the application.

 

[dlhoule]

If you want the convenience of an extra handle to kill the panel you're about to work in, a MDP wouldn't be a bad idea. However, I think from a safety standpoint, the MDP is a bit misleading because the panel is still energized if you shut off that main breaker. So, PPE would still be required.

I use MLO's every day, and don't have a problem with it. There are specific times to use the different types, it just depends on the application.

George is at least partially correct. However, the only portion energized with main breaker are the supply wires and terminations. The bus bars are not energized. It frequently is a lot more convenient to be able to turn MB off at the panel you are going to work in as opposed to going up stairs or to a separate building to do 10 minutes of work.

 

[George Stolz]

Larry, since the components you mentioned are energized, then PPE is technically required, right? It's convenient for me to just work an MLO panel hot, too, but that's not a great idea without PPE.

I'm saying, I think from a safety standpoint, you decrease the chances of getting nailed by shutting off the busses, but you're still working in a live panel, right?

 

[izak]

you are right George,

You Get to use PPE??? what state do you work in and is your employer hiring??? heh

 

[dlhoule]

Larry, since the components you mentioned are energized, then PPE is technically required, right? It's convenient for me to just work an MLO panel hot, too, but that's not a great idea without PPE.

I'm saying, I think from a safety standpoint, you decrease the chances of getting nailed by shutting off the busses, but you're still working in a live panel, right?

Yes, George, you are correct you are still working in a live panel and PPE is required. However, typically with breaker the only place there will be exposed power is at the line side of main breaker. With MLO, short of turning off all of the breakers you have power all over the place including the bus bars. A lot more potential for shock or arcing exists with MLO unless killed at the source and then you should still be using PPE until you have confirmed you have indeed turned off proper breaker or disconnect to remove power from panel altogether.

Actually, I'll have to check this but, I think once you have turned off main breaker, and confirmed breaker opened all lines with power, you can then do the work without the PPE.

 

[don_resqcapt19]

George,

Larry, since the components you mentioned are energized, then PPE is technically required, right? It's convenient for me to just work an MLO panel hot, too, but that's not a great idea without PPE.

You are not permitted to work in or on energized electrical equipment with or without PPE other than the very limited exceptions. The most notable of which is troubleshooting.
Don

 

[don_resqcapt19]

Larry,

Actually, I'll have to check this but, I think once you have turned off main breaker, and confirmed breaker opened all lines with power, you can then do the work without the PPE.

If you are working on a panel that meets the Canadian Electrical code, I would agree, but not if working on a typical US panel. The Canadian Code requires an additional interal metal cover over the line terminations.
Don

 

[dlhoule]

Larry,

If you are working on a panel that meets the Canadian Electrical code, I would agree, but not if working on a typical US panel. The Canadian Code requires an additional interal metal cover over the line terminations.
Don

Once again you are correct, Don. I was thinking of the panels used on machines in industrial plants. Unless it is a very old panel there will be no exposed live parts. In a typical US panelboard, there are times I cheat. If main breaker is fed from top of panel and I am changing breakers in bottom portion of panel, once I have confirmed I have removed the power from the bus I sometimes remove a portion of the PPE before doing the work.

I'll respond here to your previous post also. I tend to classify troubleshooting as separate category from work. We have to troubleshoot hot most of the time, but we do not work hot except under very special conditions. In my facility you are not allowed to work hot without a special permit. It is not issued to just anyone who asks for one. In the last 3 years we have issued 2 permits for hot work.

 

[wirestripper]

There is no safety issues as long as the panel is protected up stream by a main breaker sized appropriately.

The installation of a second main is a matter of preferences. Local codes however, do vary and I have heard of locals requiring the second main for reasons that I don't know.

My jurisdiction requires a outside main breaker at the meter, for example, as a result of a request to the city council by the Fire Department.

Code requires a main for 6 or more circuits as a rule, but where it goes in the feeder is a variable, as long as it is there...

I think that about covers it, based on my experiances and training. My personal preference, is to protect any run of cable that goes to a panel within a structure and the placement should be ahead of the cable run. Whether there is a second redundant main at the load center, is a matter of personal preferences and/or the local code restrictions that go beyond the NEC.

 

[coulter]

George, Don, Larry -

This application certainly sounds residential. If so, what regulatory authority requires PPE?

I agree its a good idea - I always wear mine as appropriate to the job.

carl

 

[don_resqcapt19]

Carl,

This application certainly sounds residential. If so, what regulatory authority requires PPE?

Unless you are self employeed the agency is OSHA.
Don