lamp earthing - Page 1
Forum section: electronics / beginners

author: kentroverman
author_rank: Newbie
timestamp: September 06, 2015, 02:17:06 pm
content: I am concerned about this lamp. The lamp has a metal stem that the wire runs through to the plastic socket. I am concerned that if one of the wires drop out of the socket it will contact the stem and as it is not earthed it will give a electric shock. Dont really understand why lots of these types of lamps are not earthed. Any advise will be appreciated.ThanksCliff

author: IanB
author_rank: Super Contributor
timestamp: September 06, 2015, 02:20:31 pm
content: There may be plastic sleeving on the inside to prevent any loose wires coming in contact with the metal.

author: mij59
author_rank: Frequent Contributor
timestamp: September 06, 2015, 03:27:19 pm
content: The lamp might be considered double isolated but when touching the metal there could be a tingling sensation due to capacitive coupling, use a earthed power cord and connect the metal parts to the earth wire.

author: kentroverman
author_rank: Newbie
timestamp: September 06, 2015, 05:03:58 pm
content: Thanks for the advise. Given me something to think about.

author: wraper
author_rank: Unknown
timestamp: September 06, 2015, 05:09:09 pm
content: Quote from: mij59 on September 06, 2015, 03:27:19 pmWhat capacitive coupling???This is not SMPS with Y1/Y2 capacitors, you won't feel tingling because of few pF of capacitance between wire and enclosure.

author: mij59
author_rank: Frequent Contributor
timestamp: September 07, 2015, 03:09:53 am
content: Quote from: wraper on September 06, 2015, 05:09:09 pmYes I can, am the sensitive guy, and no I am not wearing a tin foil hat.

author: tggzzz
author_rank: Super Contributor
timestamp: September 07, 2015, 08:43:14 am
content: Quote from: wraper on September 06, 2015, 05:09:09 pmThe kind of capactative coupling that gave me a very mild shock 35 years ago.It was a 19" rack instrument with earthed case, but touching the front panel gave me a shock. The engineer responsible denied it was possible but refused to touch it!.Eventually we noticed that the fron panel's hinges were plastic, so that it was electrically isolated from the rest of the case. The cure was sinple, obvious, and effective.

author: wraper
author_rank: Unknown
timestamp: September 07, 2015, 09:07:45 am
content: Quote from: tggzzz on September 07, 2015, 08:43:14 amCertainly there was more than just panel being on plastic hinges. Likely some stuff under voltage attached to the panel and leaking some current into it. If it was just single shock, that might be static electricity too.

author: wraper
author_rank: Unknown
timestamp: September 07, 2015, 09:11:58 am
content: Quote from: mij59 on September 07, 2015, 03:09:53 amYou should then get tingling from most of the modern power tools. 95+% of them are not earthed. Or any metal object lying nearby the mains cable

author: tggzzz
author_rank: Super Contributor
timestamp: September 07, 2015, 09:17:19 am
content: Quote from: wraper on September 07, 2015, 09:07:45 amNo, and no.The main chassis was properly grounded and there was no nearby power source.There was no electrical connection to anything on the front panel: it was simply a flap of aluminium that allowed access to the PCBs inside.The shock was repeatable and the strength of the shock was constant.

author: mij59
author_rank: Frequent Contributor
timestamp: September 07, 2015, 12:52:10 pm
content: Quote from: wraper on September 07, 2015, 09:11:58 amWhen powered on I do not like to touch the metal parts of my mains powered tools.Two lose isolated wires in a metal tube can have considerable capacitance, it all depends on the circumstances.