Just got zapped - Ground switch question

[loverocker]

This isn't a homebrewed amp, so it's not my fault (honest!)... I just imported a Victoria Reverberato from the US to the UK. It has a Ground switch and a three-prong cable plugged into a 110V/240V transformer. It works fine ... but...

I was just now switching it off, when I got a shock from the (metal toggle) On/Off switch. So I switched off at the wall, and now I'm wondering if the Ground switch is playing a part in this Here in the UK, we've not had such them on any/many amps, so I've never even thought about what they do, and if it might be at fault?

Any advice?

[danelectro]

why are you switching the ground? theres ground switches in some things like rack mount gear and DI boxes and such but thats a signal level ground lift..

im not sure that you want to ever lift the real mains ground.. just for that reason

[loverocker]

Um... I didn't touch the Ground switch - I was just switching the amp off via the On/Off switch when it bit me

Just to clarify - I've never had an amp with a Ground switch because they just don't appear on British amps, so I've never had one to wiggle one way or the other. In fact, the control panel on this particular widget gives no indication as to which position of the switch is On/Off/whatever...

[danelectro]

do you mean a standby switch? the only power related switches on most amps are standby and power. the power switch should switch the hot power line from the wall, not the ground. if you amp is wired for a 3 prong cable (120 or 240, doesnt matter) the ground wire is there as a safety mechanism and should never be switched.

its there incase of a power short in which a hot wire gets exposed to the chassis. when the ground wire is there (on the chassis) the exposed power wire goes to ground and not to you.

because youre being shocked by a chassis mounted (unisolated i assume) switch, id make sure your ground wire is properly placed and that it is not switched..

sorry if im misunderstanding your problem, im not sure exactly what you mean

[Dai]

a ground sw. is usually a cap about 0.047uF from either side of the two AC wires to ground or completely disconnected from both sides. I guess the questions to ask, are 1) is the outlet wired correctly? 2) is the outlet grounded? 3) are the hot and neutral wires wired correctly to the power plug? and 4) are you still shocked w/the ground switch in the other (1 or 2) positions? Take your DVM, put it on AC volts, then touch one probe, then put the other one on the chassis. Flip the ground sw. in diff. positions. The LOWEST reading is the correct one. (You might use a rubber glove or a mitten so as not to get shocked.) You shouldn't need the gr. sw. though if you have a properly grounded outlet.

[loverocker]

Thanks Dai - I'll try that this weekend. I haven't tried to 'use' the Ground switch - it's in the position it was shipped in (from the USA) and the front panel gives no clue as to which position does what (nice one Victoria!)

I'm 99.9% sure the outlet and cables are OK - they've been used with other amps without issue. I'll also do an earth continuity test between this outlet and other outlets.

danelectro - lots of US-made gear has a Ground switch. Its use remains a mystery for some of us in the rest of the world

[danelectro]

hah leave it to america to mess everything up