[modeleng] Re: FW: Question about phase converters
- From: "Andrew Houston" <andrew@xxxxxxxxxxxxxxxxx>
- To: <modeleng@xxxxxxxxxxxxx>
- Date: Sat, 4 Feb 2006 00:54:17 -0000
Peter
You've made some very good observations and I agree with some of what you've
said. No doubt with your experience, you have made a safe and effective
solution in your particular circumstances from a commercial product, which,
it appears from your description, would otherwise not have been suitable for
its intended use.
One should, however, be very careful to follow the required regulations,
even if these appear to be - in one's personal estimation - "downright
dangerous". I too am an Electronics Engineer. I'm also a Chartered
Engineer and MIEE - but with only 40 years experience vs your 50. I would
not, however, claim to be an expert in every aspect of domestic power
installations but I could - and have - used my knowledge of fundamental
electrical engineering principles - and a thorough study of the IEE Wiring
Regulations applicable at the time - to safely rewire four houses. Much as
I may think that some aspects of the current regulations - especially "Part
P" - are illogical, I am bound to act in a professional manner and follow
them.
Should there be, say, a fire in one's workshop which might be attributed to
an electrical fault, one could find oneself in serious trouble if the fire
caused injuries, death or damage to property and it could be shown that the
installation did not meet applicable standards and regulations and that you
were the cause. At the very least, I'm sure the insurance company would use
it as an excuse to withhold compensation.
In my professional career, I have been involved as an expert witness in
successful defence of litigation involving electronic equipment, which was
alleged to have started a fire causing 6.2 million dollars worth of damage.
It was a civil case in the USA and, in the circumstance, we were assumed to
be guilty and had to prove we were innocent. Luckily we could show that all
applicable standards had been followed and that the equipment had more than
adequate safety margins. More than could be said for a number of other
"electrical goods" and extension cords in the immediate area.
OK. The manufacturers may be protecting themselves in specifying VFDs as
"One Motor, One VFD". If I were cynical, I could say that they were doing
that to sell more VFDs. Irrespective, not following the manufacturers
recommendations can not only invalidate any guarantee of the product but
could be used a primary evidence of incompetent installation.
Maybe I'm being over pessimistic, but in today's "nanny state" it only takes
one Model Engineer's workshop disaster to shut down our hobby. Let's not
give anyone the ammunition. Suffice it to say that if you haven't got the
necessary experience to safely install the electrics or the knowledge to
safely modify it, you should seek professional help.
Andy
-----Original Message-----
From: modeleng-bounce@xxxxxxxxxxxxx [mailto:modeleng-bounce@xxxxxxxxxxxxx]
On Behalf Of peter.chadwick@xxxxxxxxxxx
Sent: 03 February 2006 20:10
To: modeleng@xxxxxxxxxxxxx
Subject: [modeleng] Re: FW: Question about phase converters
Andy said:
>"add some plugs or switches to change machines over and build a mobile
control box to run it with" - sorry, I don't like the sound of that wrt
Safety, EMC, manufacturers recommendations, IEE Wiring Regulations, etc,
etc.<
That's a bit dependent on how it's done. I use one variable speed drive
for both lathe and mill, since I can't use both at once.
As I said earlier, as supplied it was a total disaster - and the inverter
manufacturers recommendation about screened leads
for EMC hadn't been followed, plus the saftey issue of non-earthed metal
boxes containing switches......However, I rebuilt the
whole lot so that there are various safeguards to prevent reversal without
going through OFF, preventing the machines being
turned ON unless the appropriate start button has been pressed, and so on.
It's all run off a single 13 A plug as the motors are
relatively small. I feel confident in doing all that though, since I've
been doing electronics for the last 50 years, and a fair amount
of that at high power radio frequency. Part of which is why I regard the
new regulations as being in some cases downright
dangerous, such as in using circuit breakers on lighting circuits so that
half the house is plunged into darkness when a bulb blows
and the breaker trips!
Peter Chadwick
Usually Swindon, San Diego this week.
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