peleliu
journeyman
Reged: 01/05/08
Posts: 82
Loc: Winston-Salem, NC
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With a wall-mounted electric projection screen that has a built-in junction box for 120 vac control, what is the best way to connect it to an in-wall outlet box. The screen requires 120 vac for control with 4 wires (2 hot (one for up and one for down), a neutral and ground). I'm not sure if it is acceptable to use a flexible rubber cord (3-wire plus ground) and hardwire it through a hole in the outlet box cover plate. Or do I need a plug on the cord for installation convenience or code compliance? If so what plug? The motor draws a max of 2.4 amp.
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Gizmologist09
enthusiast
Reged: 02/08/09
Posts: 269
Loc: Palmdale, California USA
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These are usually connected to a center off. spring loaded rocker switch or a relay equipped remote interface for connection to a home automation control system. The screen control wiring can be fed into a concealed Jbox and then wired with 14-3 romex to a second box with the rocker switch and a 120volt ac feed.
The wiper (center) of the switch is the common to the AC hot, and the neutral and ground connect as usual.
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peleliu
journeyman
Reged: 01/05/08
Posts: 82
Loc: Winston-Salem, NC
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Quote:
The screen control wiring can be fed into a concealed Jbox and then wired with 14-3 romex to a second box with the rocker switch and a 120volt ac feed.
My question is about how to make the screen control wire connection from the screen to the junction box: "I'm not sure if it is acceptable to use a flexible rubber cord (3-wire plus ground) and hardwire it through a hole in the outlet box cover plate. Or do I need a plug on the cord for installation convenience or code compliance? If so what plug? The motor draws a max of 2.4 amp."
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jdevlin
Carpal Tunnel
Reged: 09/09/02
Posts: 6188
Loc: Welland Ont. Canada
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SO cable(flexible cord with rubber coating) is not suitable for use in a wall. You need to use NM or other suitable in wall cable. You must use junction boxes for all your connections as well.
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Please do not Private Message with questions that can be answered in a Forum. I will not respond.
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peleliu
journeyman
Reged: 01/05/08
Posts: 82
Loc: Winston-Salem, NC
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Quote:
SO cable(flexible cord with rubber coating) is not suitable for use in a wall. You need to use NM or other suitable in wall cable. You must use junction boxes for all your connections as well.
The screen hangs on the wall so control power must be brought to it from a wall outlet near the built-in screen junction box. Think of it as a pigtail or power cord on an appliance but it has four wires (hot up/down, neutral and ground) that are fed from a three position wall rocker switch. This wiring is external to the in-wall wiring. The wiring from the switch to the wall outlet near the screen is all in-wall.
I am asking about the method of connecting the control power from the outlet box near the screen to the screen's internal junction box. Specifically what kind of cord and can it be hard wired through the cover plate of the wall junction box or do I need a plug and what kind of plug? My original post above may state it better.
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BillJeffy
"Don't Know Squat"
Reged: 01/02/06
Posts: 4061
Loc: USA
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If I understand what your explaining,
you need a flexible cord from the wall box to the TV box...
so that it will flex when you move the screen.....Yes? No?
If that is correct, a four-wire SJ cord (very flexible) should suffice
(similar to cord on electric drill)
Being a four wire, however, limits what you could use for a 'plug'
and i expect it could run through the box cover (with hole)
using a cable connection with flex protection at box.....(rubber sleeve)
You need enough of a loop to prevent a 'hard' flex at boxes......
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Just Common Sense......
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err....I'm not a Doctor, but I'll take a LOOK ! !
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Gizmologist09
enthusiast
Reged: 02/08/09
Posts: 269
Loc: Palmdale, California USA
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OK, from a professional audio visual systems designer -me- here is the approved method. The screen wiring comes with a rubber jacketed cord with white, green and 2 other colors, sometimes red and black and sometimes red and blue.
It is legal and required by the manufacturer of the screen to terminate the attached cord through a cable clamp in either the cover plate of a concealed J-box or through a KO in a surface box. The joints are then made to approved in- wall wiring to a power source and the control legs.
The switch needs to be an SPDT momentary normally off(center off) rocker or toggle switch. Using 2 separate NO switches will void the warranty unless they are electrically interlocked such that power cannot be applied simultaneously to both the up and down control legs.
Many screen manufacturers make a 120 volt to 12 volt relay interface that includes a transformer and control circuitry. This is the most advisable method of control.
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MCA
Carpal Tunnel
Reged: 03/09/06
Posts: 2609
Loc: Illinois
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The first question I have is if flexible cord is acceptable in this situation, it appears that you say it is.
Flexible cord with 4 wires is available at electrical supply stores (if not included), but it will be called for example "14/4" (the ground wire counts as a wire in the flexible cord markings, but I beleive they changed the markings and may say "14 AWG 4 conductor" on the jacket) unlike building wiring where a cable is called "14/3 plus ground". If there is a 1/2" conduit knock out you can use flexible conduit with individual THHN wires and connect it to a metal faceplate with a 1/2" knock out on it, if it is frequently moving then you want to use stranded wire.
Edited by MCA (02/04/10 10:38 PM)
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Gizmologist09
enthusiast
Reged: 02/08/09
Posts: 269
Loc: Palmdale, California USA
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Yes, the screen's attached SJO cord is short and designed ONLY to go as far as necessary to reach whatever control system is used, whether a 120v up/down rocker or the low voltage controller interface. The cord length is designed to be only long enough to reach the mounting surface of the screen where a Jbox is mounted. Depending on the available power, the first Jbox may have the 120 volt feed as well as the common and 2 switch legs for the U/D controls or the wiring can be extended via romex or THHN in conduit to the end control point.
Although it is permissible to surface mount the SJO cord to enter a surface mount switchbox, it is rarely done as it looks terrible in most circumstances.
At no time is it permissible to use a 4 conductor AC plug or 2 standard AC plugs to terminate the control harness as this would entail having switched outlet(s).
It is NOT (as correctly noted) to run inside a wall.
If the control desired is simply a SPDT rocker, then we do use 14/3 w/gnd romex to go from the 1st Jbox terminating the SJO cord to wherever the control is mounted, sometimes on the opposite end of the room or a control room.
Edited by Gizmologist09 (02/05/10 08:46 AM)
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3phase
Electrician
Reged: 09/09/02
Posts: 6673
Loc: Licensed Electrical Contractor...
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From my industrial background I would say most flex conduit"s might not be a good fit either. Bend radius and constant movement might create problems. I know metal would not work and plastic might but I would think the tight radius needed might exceed code min and could cause a premature failure.
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Rule of thumb,Keep your thumb from under the hammer!
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