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Cable Entry/Strain Relief Identification From Hole Pattern?

DerStrom8

Super Moderator
Greetings all,

I have been working on restoring an old Variac control panel and am at the point of installing my new power cable. The original box (which I am reusing) had a hole pattern cut into the rear of it where the power cord entered the unit, but there was no grommet or strain relief. I was curious if anyone recognizes the hole pattern and could recommend a replacement part? Here is the existing hole pattern:

1619366972284.png

The center hole is 1.125" diameter, and the two smaller mounting holes on the sides are 1.75" center-to-center. Anyone seen these before?

Thanks,
Matt
 

nsaspook

Well-Known Member
Most Helpful Member
Looks similar to the old plugs and sockets

 

DerStrom8

Super Moderator
Looks similar to the old plugs and sockets

Someone suggested a twist-lock recessed plug, like the NEMA L7-15, but those seem a bit too large for this knockout. This unit houses a 20A variac, so presumably it was designed with a 20A plug originally. Not finding many panel-mount plugs that size and rated for that current though.
 

DerStrom8

Super Moderator
It would almost fit a NEMA 5-20 recessed receptacle, though those still seem to be on the large side.
 

KeepItSimpleStupid

Well-Known Member
Most Helpful Member
I was thinking of this: https://hubbellcdn.com/specsheet/WIRING_HBL5278C_spec.pdf, but it isn't.

There was a connector that I purchased from newark.com, probably Hubbell that was basically a flange mount twist lock. The wierd thing about the specification was 125/250, but it was grounding.

This https://www.mcmaster.com/6755K222/ comes close mounting wise, but it's not grounding.

Here https://www.mcmaster.com/6755K172/ is the grounded version. The one I used was dual marked like the one above.

I needed a locking power connector because power came from wall mounted outlets in an array of surface mounted raceways.
The equipment was about 15-20' away but we had both 120 and 208 stuff. Guess what, either variacs or temperature controllers. If you removed a piece of equipment to work on it, you used a shorter power cord. It was too difficult to undo.

Since they were built by me, it was possible to convert to 120/240 relatively easy. Maybe I used 240 style breakers, but only connected 1/2 of them for the variacs. Heat tape. application.

For the temperature controllers which needed a "positive disconnect", I would include a 120V relay and a transformer with a 120/208 primary to 120V secondary and two fuseholders where one would not be used.

One or two separate over temperature units would disconnect the power via the contactor. This, was the only system that required over temperature protection of this magnitude. One type would actually mount in the back of the case. The rack was open, so no big deal.

The controllers I built also offered off on power glitch or not depending on the application. That was front panel set.

The internal wiring change wasn't just one jumper, but because I liked to make appliances, I designed it in. When/if the reactor was de-commishioned the parts would still be viable.

I made tabletop temperature control boxes that were there 28 years later. newer controllers were a little longer than the box.
The front panel had a real 30A disconnect. On/Off and Int/Ext 0-5 setpoint in. ON/OFF allowed you to see the temperature when turned off. The disconnect allowed the output to be potential free.

The rear panel had a panel mounted TC input AND a grommet for a extension wire pigtail.

Setpoint in, Measured value was available on a screw terminal strip. Chart recorder stuff when used for manual tuning.

There was a locking current limit potentiometer.

I don't remember what I did for power in/power out, but I think I had cable and receptacles for out and cable for in.

Controllers were 1/4 DIN. Some newer 1/8 DIN controllers were put into the same box.
 

DerStrom8

Super Moderator

KeepItSimpleStupid

Well-Known Member
Most Helpful Member
It won't make use of the two holes on the side but should serve the purpose nicely.
Matt:

I drilled the top of a box for feet once, so I just added screws to make it look nicer. I was making an in-house designed item for someone else Fill the hole with a screw. It doesn't have to be functional, right?
 

vtech

Active Member
Late to this thread... for what its worth, I happened to work with several legacy brand 60Hz/400Hz Variacs in Avionics field, most of which are either out of biz. or taken over by other firms. Across the board while there is a separate input line, there is a similar opening on the right side side of the case meant for "output"

Variac.jpg
 

DerStrom8

Super Moderator
Late to this thread... for what its worth, I happened to work with several legacy brand 60Hz/400Hz Variacs in Avionics field, most of which are either out of biz. or taken over by other firms. Across the board while there is a separate input line, there is a similar opening on the right side side of the case meant for "output"

View attachment 131347
That looks about right, though this pattern is on the rear. Two separate receptacles were used on the front of the panel for outputs, so whatever the holes were originally used for I suspect would have been the supply connection.
 

unclejed613

Well-Known Member
Most Helpful Member
it could also be a split clamp strain relief. it's a sheet metal plate with one half of the clamp that mounts to the panel, then the other half of the clamp is attached to the stationary clamp with two screws and tightened down on the cable. i've seen them on older pieces of equipment, but i don't think they're made anymore.
 

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