Wiring up a sub panel

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Old 03-04-20, 11:46 AM
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Wiring up a sub panel

All, I am new to the forum. I'm a jack of all trades and a master of none, but I am more than willing to put in time and effort to learn something and get it right. Just recently I ripped out my old boiler and replaced it with an ultra high efficiency boiler (wall hanging) and had no idea what I was getting myself into. Anyway, it works great and I learned a lot of info along the way.
​​​​​ That said, let me ask my question.
I am kind of being coached by a coworker who has his electrical engineering degree. He has me running a 100 amp sub panel which in this case is a main service panel and turns out is acceptable as a sub panel as well. He had me run 2-2-2-4 wire and I am getting ready to pull it through into the panel. The panel has been cut into a sheetrocked wall, so the cavity is not exposed. I have access to the top of the wall that this panel is located on, so I will drill an access hole and drop the wire in this way. Wire connectors... is it against code to have the screws inside the cabinet? Otherwise I'm not sure without cutting the entire cavity above the panel out, how you would tighten the screws if not in the cabinet. Also, if I were to pull other wires, I am assuming I would run into the same dilemma. I mean I can picture putting in several connectors for potential-future pulls, but even this would still leave the issue of tightening the screws if they are hidden in the cavity.

also, thank you in advance for any info you can give me on this.
 

Last edited by Sponger76; 03-04-20 at 01:07 PM.
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Old 03-04-20, 02:15 PM
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If the 2-2-2-4 is aluminum the over current protection is to be no more than 90 amps. The feed to a subpanel is a branch feeder and the amp capacity is set by NEC table 310.15(B)(16) which is 90A at 75deg.C. The feeding breaker needs to be a 90A and the main breaker in the subpanel is fine being a 100A because it's just a disconnect. The NM two piece clam shell type clamps can be installed from the inside with the clamping screws inside the panel.
 

Last edited by pattenp; 03-04-20 at 05:00 PM.
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Old 03-04-20, 03:53 PM
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If you canít get to the connector screws, how can you get to the locknuts?
 
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Old 03-04-20, 03:59 PM
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The sub panel will not be getting a main breaker(wiring directly into the lugs provided). If I need to lower the main panel breaker to 90, that is fine. This sub panel will feed my woodshop while I'm in it, or a 3 season room when I am in there. The 3 season room will be lighting l, a fridge and some outlets, but nothing that should draw a lot of current. The wood shop will have a few items on it and it looks like the table saw is my highest draw of current at 13 amps (I'm sure a little higher under stress), but at best, one machine is turned on, one is turned off, etc...
 
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Old 03-04-20, 04:03 PM
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Also, I understand the point you are driving home. Even if I never get to the max operating temps, I will eventually sell the place and I need to make sure that the house doesn't burn down due to incorrect wiring
 
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Old 03-04-20, 04:59 PM
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telecom guy
If you can’t get to the connector screws, how can you get to the locknuts?
That's why I said use the 2 piece clam shell type NM clamps. No lock nut.
 
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Old 03-04-20, 05:14 PM
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Welcome to the forums.

Do you have a 200A service ?
What does that boiler draw ?

When I pull cables thru a wall to a panel..... I put the connector on without the locknut, pull the cable into the panel and put the locknut on. Can be a little more difficult with larger cable as the hole at the top of the wall needs to be somewhat larger.

 
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Old 03-04-20, 05:24 PM
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The boiler is propane fed and draws less than 10a per the spec sheet. My coworker and I did an add up of the main panel and even with the 100amp (switching to 90 amp tomorrow), we calculated that I was below the max for my 200amp service in my main panel.
 
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Old 03-04-20, 05:49 PM
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Great...... sounds like a plan.
 
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Old 03-05-20, 07:05 AM
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The clam style. I totally forgot those even exist. I have come across them and thought "what the heck is this?" Now I know what they are intended for. Thank you for the info all

 
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Old 03-05-20, 07:56 AM
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You take out the clamping screws of the the 2 piece NM clamp and insert the 2 halves from the inside of the panel and reinstall the screws. I only use those clamps when adding a circuit to an existing panel in the rare case I can't use a regular NM clamp.
 
 

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