Safe or Not Safe? Mailbox Lamp

1 reply [Last post]
williamebyrd's picture
Joined: 2016-11-03

I'm replacing a mailbox lamp for a friend. I'm getting 120V across the black and bare. I get no voltage across black and white. I'm assuming that the neutral is broken, probably underground. An electrician estimated $500 to dig a trench and replace the cable from house to mailbox. He couldn't advise me (for liability reasons) when I asked if black to bare would pose any safety hazards. So I'm researching for the answer. I was thinking that I would wire it that way, making sure that the breaker controlling it was GFI protected. The mailbox and lamp and post are all metal. I'm just not impressed with solar/LED arrangements.

Any advice? I appreciate any help.

jbd172002's picture
Joined: 2014-01-06

In short, I don't think it's safe nor can it be made safe under existing conditions based solely on what you've said here. It is difficult without seeing/knowing more so I have to make some educated guesses based on what I've seen in the field.

Based on the fact that you have a bare wire I am assuming it is some type of NM (non-metallic) cable (i.e., Romex). It's either typical NM, which is only rated for indoor use and certainly in no case for underground use, or it is a type of cable called UF, which is rated for underground use and has a gray jacket. Just because NM-B cable isn't rated for outdoor and underground use doesn't mean you won't find it, a lot. Sometimes it lasts for years, but it deteriorates quickly underground and should never be considered safe.

Since the neutral wire has gone bad, so to speak, it makes me wonder what condition the rest of the cable is in. It might fail in short order. Also, if it's already damaged if you put a GFCI on it, it very well might trip immediately due to leakage underground. Either way, Code compliant or not (read NOT, you can't make it that way with that wire), there is no safe way to reuse that wire for a 120V circuit. Given the metal post, etc. and being outside it is foolish to not install a safety ground. Furthermore you don't know where the wire terminates at the house and unless you were able to remove that single wire from the rest of the ground system, applying a load to it would then put unsafe current back on the rest of the ground system in other parts of the house.

If you could possibly isolate the wire at both ends I might give some consideration to using a low voltage transformer, like 12V and use landscape lighting or some other 12V type lamp/fixture at the mailbox.
That would then afford you the hardwired system you desire but with a voltage and system designed and safe to operated on two wires. Also if the wire underground failed it's much less likely to kill someone.

These are my thoughts. I am a journeyman electrician in Kansas and do service work and new installation for residential, commercial and industrial.

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