Why some electrical boxes have clamps for the Romex and others don't (?)

[Stephen Tashiro]

Why are wires clamped as they enter some types of electrical boxes and not clamped when they enter other types?

Boxes for electrical outlets and switches usually have some way to clamp the Romex wires as they enter the box. However, breaker boxes and service disconnect boxes don't have built-in clamps. I don't recall seeing a panel box where any kind of clamps were added to the holes in the box.

[Rod Sheridan]

Why are wires clamped as they enter some types of electrical boxes and not clamped when they enter other types?

Boxes for electrical outlets and switches usually have some way to clamp the Romex wires as they enter the box. However, breaker boxes and service disconnect boxes don't have built-in clamps. I don't recall seeing a panel box where any kind of clamps were added to the holes in the box.

There are 2 reasons for that.

1) The manufacturer has no idea what size cables will be installed so they can't provide built in clamps.

2) The manufacturer has no idea whether you'll be using Romex, Bx, Teck or conduit so once again no built in clamps.

regards, Rod.

[Paul F Franklin]

Plastic boxes for single devices (switches, receptacles, etc. do not require clamps at the box for use with Romex, but the romex must be secured near the box, say with a staple to the framing within (IIRC) 8-12 inches. A proper fitting is required when romex enters a metal box, including breaker boxes and the like, although some metal boxes have built in clamps. If romex goes through a knockout into a metal box, it must have a proper clamp fitting, metal or plastic.

[Bill Dufour]

All the breaker boxes I have ever seen are metal not plastic. It is easy and cheap to mold cable clamps into a plastic box. For a metal box there is no cheap way to add a cable clamp at the factory. Every hole that is punched open in a box has to be plugged. My big panel in the shop probably has over 50 knock out locations on it. 6-10 top and bottom, 20 or so on each side, 10-15 on the back. Many of these are both 1/2 and 3/4. with bigger ones available top and bottom. If these all had clamps installed there would not be much free space inside the box.
Bil lD.

[Brian Elfert]

Boxes for electrical outlets and switches usually have some way to clamp the Romex wires as they enter the box. However, breaker boxes and service disconnect boxes don't have built-in clamps. I don't recall seeing a panel box where any kind of clamps were added to the holes in the box.

Are you seeing breaker panels (load centers) installed without clamps for all of the cables entering the breaker panel? The job must not be inspected because only a blind electrical inspector would allow such a job to pass.

I have done plenty of electrical work in the two houses I have owned and I always use clamps on the wires entering the load center.

[Frank Pratt]

Are you seeing breaker panels (load centers) installed without clamps for all of the cables entering the breaker panel? The job must not be inspected because only a blind electrical inspector would allow such a job to pass.

I have done plenty of electrical work in the two houses I have owned and I always use clamps on the wires entering the load center.

I think he meant that the panels don't come from the factory fitted with clamps.

[Stephen Tashiro]

If romex goes through a knockout into a metal box, it must have a proper clamp fitting, metal or plastic.


Do clamps for "non metallic cable" count as proper clamps for Romex? e.g. https://www.homedepot.com/p/Halex-3-8-in-Non-Metallic-NM-Twin-Screw-Cable-Clamp-Connectors-5-Pack-20511/100133208?MERCH=REC-_-pipsem-_-100132132-_-100133208-_-N

That type of clamp is difficult to use when the knockout is through the back of a disconnect box. There's no room to get a screwdriver on the head of the screws.

[Rollie Meyers]

Single gang plastic nail on boxes do not normally have strain relief connectors and are not required when stapled within 8" of the box, single gang cut-in (old work) boxes do require strain relief connectors because the cable is not supported when fished in the wall cavity. Personally I prefer metal boxes unless handy/gem boxes are used.

[Frank Pratt]

Single gang plastic nail on boxes do not normally have strain relief connectors and are not required when stapled within 8" of the box, single gang cut-in (old work) boxes do require strain relief connectors because the cable is not supported when fished in the wall cavity. Personally I prefer metal boxes unless handy/gem boxes are used.

Not in all areas. Here a connector is required where ever a cable enters a box. Period?

I don't like plastic boxes either, and they really have never caught on here. Nobody uses them except for DIYers. Over the years we've tried out many different plastic boxes & always go back to metal. They are better in almost every way.

[Mike Cutler]

I don't like plastic boxes either, and they really have never caught on here. Nobody uses them except for DIYers. Over the years we've tried out many different plastic boxes & always go back to metal. They are better in almost every way.

I don't like them either. They're used everywhere here, and pass inspection as is, but they're cheap. I'd rather have metal also.

[Paul F Franklin]

I don't like the cheap thin light blue plastic boxes; the sides bend easily and they never seem to line up properly with the sheetrock. I am fine with the heavier wall cast plastic/fiberglass boxes. No need for a ground bond wire (although this is less of an issue with self grounding devices that are common now) and no clamp needed on new work.

[Rollie Meyers]

Not in all areas. Here a connector is required where ever a cable enters a box. Period?

I don't like plastic boxes either, and they really have never caught on here. Nobody uses them except for DIYers. Over the years we've tried out many different plastic boxes & always go back to metal. They are better in almost every way.


I can only go by NEC rules since California is under the 2014 NEC and do not have a copy of the CEC, and the NEC allows single gang plastic boxes to be used W/O strain relief connectors as long as the cable is stapled within 8" of the box and multiple cable entries are also permitted. NEC article 314.17(C) Exception 2014 edition. As to metal boxes I prefer them as long a they are proper ones, when I see handy / gem boxes in use I know the wiring is a mess, but 4 square boxes with the correct plaster ring for concealed installations or raised covers for surface mounting, as to "proper rings" that means a ring 1/8" deeper then the finish material, so for 1/2" drywall use a 5/8" raised ring, and for 5/8" drywall a 3/4" raised ring, which will leave it flush with the surface rather then 1/8" back, I hate floating receptacles so want the box or ring flush with the surface.

[Brian Elfert]

I think he meant that the panels don't come from the factory fitted with clamps.

I misread the OP's post then. The reason metal boxes/panels don't come with clamps is there are so many types of connections that could be made to a metal box. Are you using NM-B, PVC, rigid, BX, or EMT to bring wire into the box/panel? Each requires something different to connect to the box/panel.

The value packs that include a load center and breakers aren't adding much value these days. To be code legal almost all breakers need to AFCI. There isn't much use for the regular breakers that come in a value pack anymore.