110v

FatAlan · Sep 28, 2016

Probably silly question of the week, but why do trades folk tend to use 110v power tools running off those boxy have transformer thingys rather than the standard 230v? Is it down to safety, i.e. lower voltage or economy or something else? Note the technical lingo!
As a newbie / trainee please expect a raft of similar type questions.

Rpa07 · Sep 28, 2016

110v transformers are centre tapped so they will only have a touch voltage of 55volts. This goes along with the human touch safety limits that you can read a bout on this forum through searches and through the books on additional protection/ rcds and site safety.

Wilko · Sep 28, 2016

Hi - yes safety concern drives the use of centre tapped 110v tx on site. AFAIK, no one has been electrocuted when they have been used.

Karin · Sep 28, 2016

as i understand it it's inherently pretty safe even under fault conditions as the shock voltage wont exceed 40V.

more dangerours 230V supplies rely on protective measures that may be hard to guarantee on site.

Risteard · Sep 29, 2016

Rpa07 said:
110v transformers are centre tapped so they will only have a touch voltage of 55volts.

Actually the touch voltage will be much lower. Even with the three-phase variant of Reduced Low Voltage (RLV) which has a phase to Earth voltage of 63.5V the touch voltage will be only around 30V.

FatAlan · Sep 29, 2016

Thanks for the concise answers.

amlu · Oct 1, 2016

tends to be enforced on bigger sites by elf&safety bods, together with hi-vis, cscs/ecs and hard hats. self employed on private jobs do not give a damn, 230v for me no point lugging heavy yellow box around.

FatAlan · Oct 2, 2016

Just looking at The Electricians Guide to Building Regs. BS7671 recommends 110v single phase centre- tapped (whatever that means?) 55v to earth supplies for portable hand lamps and hand tools, and local lighting up to 2 kw. As Rpa07 above.
Thanks again.

Richard Burns · Oct 2, 2016

Centre tapped transformer means the 0V point is the centre of the coil and there is 55V difference to either end of the coil, therefore coil end to end is 110V but touching any one pole a person will only experience 55V.