DIY lamp project
December 23, 2011 12:02 PM   Subscribe

Do I have everything I need to safely put together this lamp without burning my apartment down?

So I'm building a DIY lamp due to some inspiration from the interwebz. I HATE diddling around with electricity as a result of being shocked by some stage lighting many years ago. It has left me a bit trigger shy even when doing simple things like changing a switch plate. I know...silly. I have a good understanding of basic electrical circuits, etc, but I would like someone who doesn't second guess themselves constantly in this subject to let me know if I've forgotten anything...anything. I bought two cord sets with a 75W candelabra socket and interrupter dial switch. They will need to be cut at certain intervals to fit inside this which is constructed entirely of iron plumbers pipe. The sections will be spliced together as they are layed out in the pic. I'm planning on simply twisting them and then wrapping with electrical tape, then heatshrinking over the tape. So, what am I forgetting if anything?
posted by ps_im_awesome to Home & Garden (10 answers total)
I don't know how much I'd trust twisting+taping over the long term. Since you're already heatshrinking the splices, could you solder+heatshrink instead?

Adding some strain relief somewhere (in the form of a cable clamp or something) so that when the cord inevitably gets yanked or tripped over it doesn't pull the innards apart would be a good idea. This would also help keep the splices from flexing in normal use (and possibly coming apart).
posted by hattifattener at 12:58 PM on December 23, 2011

>I'm planning on simply twisting them and then wrapping with electrical tape, then heatshrinking over the tape.

Nope. Get a copy of Wiring Simplified, and do your splices right.

Also, do you know the difference between the hot and the neutral? If not, see the comment about wiring simplified, above. Switch the hot, not the neutral.

Also, strain relief for the cord, where it goes into the base. See "underwriter's knot".
posted by the Real Dan at 1:03 PM on December 23, 2011

Having a non-inspectable splice in wiring is not exactly up to code, but you should be okay as long as you make the connections secure and well insulated. If you have room, wire nuts with tape to secure them would be better than just twisting the wires together (unless you solder them).

However, you should make sure that you have the polarity of the wire correct. The neutral wire is one connected to the wide blade on the plug. This should go to the cylindrical screw part of the socket. The hot wire is the small blade on the plug and it should go to the button in the bottom of the socket.

Likewise, when you put on the switch, the switch should cut the hot wire to the small blade, not the neutral wire.

If you don't have an ohm meter to verify your connections, you can do it by carefully tracing each wire visually from plug to socket.

As hattifattener said, you should have some sort of strain relief to prevent tugging the splice apart.
posted by JackFlash at 1:04 PM on December 23, 2011

Firstly: heatshrink, or tape. Not both.

Secondly: wire nuts would be slightly better than twisting. Screw terminals would be better again. Soldering would be best.

Thirdly: I'd be more worried about the use of metal pipe myself. I don't know about the US, but there's almost no way in hell that'd be legal in Australia unless the pipe itself was earthed.
posted by Pinback at 1:56 PM on December 23, 2011

I don't know about the US, but there's almost no way in hell that'd be legal in Australia unless the pipe itself was earthed.

In the U.S. most portable lamps do not have an earth ground. They have a two prong plug with only neutral and ground. Many have metal poles supporting them with the wires going through the pole, so this application would not be unusual.
posted by JackFlash at 2:42 PM on December 23, 2011

thanks all so far. I do know about polarity and have taken that into consideration. also, I will solder the splices as well - there is simply no room for nuts. as was noted, there is a concern of having a splice inside the lamp that is not accessible. add to that the conductivity of the body and possible movement of the cord, I was considering pumping the pipe full of expanding foam insulation after the cord is in place. this would add insulation and stay any movement. thoughts?
posted by ps_im_awesome at 3:47 PM on December 23, 2011

I wouldn't do anything that would make it impossible to remove the wire later for repair.
posted by dhartung at 5:52 PM on December 23, 2011

I'd think soldering, then heat shrinking each wire, then heatshrinking the splice as a whole would suffice. Remember to slide the heatshrink onto the wire before soldering!
posted by chazlarson at 9:44 PM on December 23, 2011

As JackFlash says, many lamps are sold in the US with basically the construction ps_im_awesome is putting together— two-prong (no safety ground) plug, metal-tube body. It would make me feel better to have the body earthed so that if the splice does pull apart it can't electrify the body of the lamp, but if the splice is solid and there's strain relief at the end, it's apparently good enough to sell. The thing is, I can't think of a good way to incorporate a safety ground into the design. You'd need to use a 3-prong plug so you could attach the ground to the body of the lamp, but then you'd have to use a different style of switch— something mounted on the body rather than the in-line style.
posted by hattifattener at 1:00 AM on December 24, 2011

Presumably commercially-constructed 2-pin lamps of metal construction would also meet the relevant standards (i.e. insulation rating, separation distances, switch & socket construction, etc.) for double-insulation.

It's not so much about earthing the metal, it's about making damned sure (from both a legal and personal safety PoV) that there's no way in hell the metal could become live. Wire nuts and electrician's tape fail badly on that count, and an underwriter's knot used inside an appliance almost encourages it.
posted by Pinback at 2:45 PM on December 25, 2011

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