Install of new nema 14-50r next to load center


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Old 11-21-22, 03:57 PM
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Install of new nema 14-50r next to load center

Recetly, I am in the process of installing a nema 14-50R (receptacle) which is rated for up to 50Amps. The double pole circuit breaker itself is rated for 45amps. The cable is nominally rated for up to 55amps (6/3).

I am mostly familiar with nm-b (romex) cable, bx, thhn, etc. In a nec publication, the table 310.15 shows the ampacity for current carrying conductors (in cables, raceways, conduits) but this tables does not mention nm-b (or romex).

The cables I bought has 3 current carrying conductors (and ground) and is rated for up to 55 amps. It is made by Southwire, and is named Romex Simpull . Looking in the aforementioned table, the best fit would likely be the first column and seventh row: which shows 55 amps, thus likely the TW type of cable. UF probably means some type of underground rated cable. Is that a correct assumption? In other words, TW = nm-b?

Below is the aforementioned table:


Also, the nema 14-50R receptacle will used in the garage whereby the load center is located. So, the installation is very straightforward. Codes and regulations can be finicky sometimes; so, I was wondering if there would be any problem in installing the receptacle right below the panel (rectangle pointed by arrow) besides the other regular receptacle, as shown in the pic below:



 
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Old 11-21-22, 06:48 PM
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In the nec, nm is stated to use the 60deg.C column for sizing even though nm is not a conductor type listed in the table.
See NEC 334.80. TW is not nm.
 
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Old 11-28-22, 11:45 AM
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You can use that plastic snap-in fitting, or use the NM clamp and simply clamp it to the wire before feeding it into the panel. Then attach the locknut like usual. Both are code-acceptable methods.

NEC requires 6" extending out from the front of the box, but I'm sure no one is going to take a measuring tape to confirm you are accurate. IMO, on such a short run, it's not like it's a huge issue if you need to make changes. If it were across the house, I'd be more concerned about a few extra inches for future changes.

Also, technically the way you're exiting that box isn't compliant with the way the box is listed. It should be exiting through the existing wire clamps as you're not allowed to drill boxes in general. But, similar to the above statement, I personally wouldn't have much heartburn with it as the clamp is securing the cable safely.
 
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Old 11-28-22, 08:09 PM
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I believe that the side of the clamp with screws should face down, but even if it faces up (inside the panel) if I was to tighten the screw it would not fit. With screws side facing down, it would imply removing more drywall (what I really don't want to do).
Install the cable clamp on the cable first before inserting it into the panel with the locknut taken off. Slide the wire into the panel and secure the cable clamp using the locknut. Loosen the screws in the plastic box and remove any slack as needed. Retighten the plastic box cable clamp.
 
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Old 12-02-22, 08:56 AM
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In a detached structure subpanel with an isolated neutral bar the grounding electrode conductor from the ground rods connects to the ground bar, not to the isolated neutral bar.
 
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Old 11-21-22, 06:52 PM
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NM-b cable has THHN wires in it but is limited to the 60-degree column for ampacity. At the 60-degree column #6 is rated for 55 amps. Code allows to go up to the next size breaker as 55 amps is not a standard size breaker. However, a 50 amp (or your 45) breaker is fine as well.

Yes, you can install the receptacle under the panel. You should use a 2 gang plastic remodel box unless you want to open the drywall. Make sure to use the proper NM cable connectors to attach the cable to the panel.
 
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Old 11-22-22, 12:43 AM
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Also, just on a side note. Looking at the panel the bar of the left side which is the ground bar. The bar is on insulators which separates it from the metal panel. I can't see because of the wires in the way but is there a grounding screw or grounding strap connecting from the ground bar to the metal cabinet?
 
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Old 11-27-22, 11:22 PM
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Good to know that. But they should at least allude somewhere in the table or footnotes that the 60 degrees columns would apply to nm-b/romex since that is what is used in the vast majority of the cases nowadays.

I am using a 45amps breaker because it was easier to find and had a better price point. Besides, it is very unlikely to there be a need for more than 40 amps. The cable is so short in this cases that I went with 6/3.

I am planning on installing a new work electrical box (not a retrofit type) due to the fact that the spot for the electrical box is right beside a stud. It is a dual gang pvc box with depth adjustment, 34 cu inches and about 3 inches of depth. I don't feel confortable installing a high voltage receptacle in something as flimsy and weak as sheetrock. Below is a pic of the box:



My understanding is that about 3 inches of wires should be protruding from the opening of the box. I am having a hard time fitting (or cramming) an extra 3 inches of wire of such gauge (6 awg) inside that box.


On another issue related to securing the cable to the panel:



I believe that the side of the clamp with screws should face down, but even if it faces up (inside the panel) if I was to tighten the screw it would not fit. With screws side facing down, it would imply removing more drywall (what I really don't want to do). Would the following type of cable clamp be adequate for that type of installation?

https://www.lowes.com/pd/Sigma-Elect...m0-_-10078-_-0


(Sigma ProConnex 3/4-in Plastic Snap-in Connector Conduit Fittings)


AFJES: The ground bar is connected to the panel encasement via screws. And it is connected to a ground rod and bonded to the neutral.

NOTE: Sorry about the delay in following up. I did not realize that there have been responses to the thread until recently.
 
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Old 11-28-22, 05:05 PM
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The ground bar is connected to the panel encasement via screws. And it is connected to a ground rod and bonded to the neutral.
If the main service panel the ground rod should be connected through the Grounding Electrode Conductor to the neutral bus, not the ground bar. And then the neutral bus should be bonded to the panel box and ground bar.
 
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Old 11-28-22, 08:17 PM
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If the main service panel the ground rod should be connected through the Grounding Electrode Conductor to the neutral bus, not the ground bar. And then the neutral bus should be bonded to the panel box and ground bar.
It has been a long time since I installed an electrical panel. My understanding is that the ground conductor coming from the ground rod needs to be connected to the ground bus. And the chassis/panel is grounded.

My understanding is that AFJES was concerned about the panel/chassis itself not being grounded. But it is grounded.
 

Last edited by tk3000; 11-28-22 at 09:17 PM. Reason: complement the info
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Old 11-28-22, 08:57 PM
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You can use that plastic snap-in fitting, or use the NM clamp and simply clamp it to the wire before feeding it into the panel. Then attach the locknut like usual. Both are code-acceptable methods.

NEC requires 6" extending out from the front of the box, but I'm sure no one is going to take a measuring tape to confirm you are accurate. IMO, on such a short run, it's not like it's a huge issue if you need to make changes. If it were across the house, I'd be more concerned about a few extra inches for future changes.

Also, technically the way you're exiting that box isn't compliant with the way the box is listed. It should be exiting through the existing wire clamps as you're not allowed to drill boxes in general. But, similar to the above statement, I personally wouldn't have much heartburn with it as the clamp is securing the cable safely.
Good to know that plastic snap-in fitting would be acceptable. Clamping to the cable first sounds like a good approach, I will give it a try.

I used to get confused about whether the 6" of wire would extend from the point of entry in the box (raceway or cable sheathing) or would be measured from the opening in the box. It seems that the 6" is as measured from the point of entry, but at least 3" should extend from the opening of the box. If 6" is as measured from the opening of the box, I would be screwed in this case considering how difficult it would be to fit that amount and type of wire inside the box.

The hole and clamp on the side of the box as shown in the pic are part of the box design. I did not drill the hole there.
 
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Old 11-28-22, 09:03 PM
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Tolyn Ironhand:

That is really good hint and approach. I will give it a try
 
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Old 11-30-22, 05:10 PM
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My understanding is that the ground conductor coming from the ground rod needs to be connected to the ground bus. And the chassis/panel is grounded.
Nope. The idea is to solidly ground the neutral conductor so the Grounding Electrode Conductor should be terminated on the neutral bus. There is a lug just for this. The green neutral bonding screw that is usually shipped loose then gets installed to bond the grounded neutral bus to the panel box thus grounding it. When a ground bar is used at the main service panel (which isn't required) only the Equipment Grounding Conductors are terminated on that ground bar. This is the procedure for the main service panel, subpanels are slightly different.
 
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Old 12-02-22, 05:47 PM
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In a detached structure subpanel with an isolated neutral bar the grounding electrode conductor from the ground rods connects to the ground bar, not to the isolated neutral bar.
This is not a sub-panel, but the main panel.

In this case, neutral and ground interconnected. The main difference between neutral and ground is that the neutral is alive -- connected to the center-tap of the secondary transformer. Current does alternate between the hot and the neutral. Also, the resistance to the passage of current to the ground and neutral differs.
 
 

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