Re: 230V to 110VAC isolation transformer



"Martin Crossley" <Martin@xxxxxxxxxxxxxxxxxxxxxxxxxx> wrote in message
news:13s93deq0olv2ae@xxxxxxxxxxxxxxxxxxxxx
Phil Allison wrote:
"Iain Churches "

I share a workshop with a couple of guitar amp techs.
They are frequently brought American guitar amps for
repair or service. Many of these have been bought straight
from the US and have a 110V mains transformer. The usual
solution seems to be the use of an isolation transformer, which
has a standard European schuko plug with no ground on the
primary side, and a two pin US style output socket on the secondary
side. There is no ground or ground terminal.


** Since all guitar amps made in the USA since the early 1970s have 3
pin plugs on the supply lead - the above simply cannot be true (a 3
pin plug will not fit into a 2 pin outlet).

The vast majority of pre 70s models will have had a 3 core cable and
3 pin US plug fitted by now - for the added safety that provides.
This has been standard practice in the US for decades.

If a 120 volt guitar amp is found with the old 2 pin US plug fitted, the
ONLY responsible action for a repair tech to take is to change
the lead and plug to a 3 wire US type.

Obviously, the techs this Iain cretin knows are ignorant, reckless
fuckwits.

No, they are not!

It is "Protection by Electrical Separation" and is an acceptable method of
protection against indirect contact according to British Wiring Regs
(BS7671) which are harmonised with most EU regs:

http://www.iee.org/Publish/WireRegs/WiringMatters/Documents/Issue18/2006_18_spring_wiring_matters_supply_to_portable_and_handheld_equipment.pdf



Just like him.

The correct procedure is to always use an *isolation* step down that
includes the protective earth on the inlet and outlet when servicing
US made 120 volt, guitar amps.



From the above document:
"Regulation 413-06-04 requires that no exposed conductive-part of the
separated circuit shall be connected to either the protective conductor of
the source circuit, or to any exposed-conductive-parts of any other
circuit."

Martin.


This is also what owners of US made guitar amps need to have if they
use them outside the USA in any 230 /240 volt country.



Hello Martin. Thanks for your interesting and detailed reply.

Phil, as is his habity, seems to have misconstrued the whole
question, and could save himself several bouts of apoplexy
if he bothered to read the question more carefully, or ask for
clarification, if the OP was unclear.

My question was not just what the techs can use (all service
benches here in Scandinavia must be fed by isolated 230VAC
with a leakage current trip). Also, every tech in the workshop
which I share has a variac, and so running a 110V amplifier
is no problem.

But these isolation transformers are supplied to the owners
of the 110V amplifier as being a safe and legal way to use
them on a 230V mains supply.

Best regards
Iain




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