[modeleng] Re: NVR connections

Dave

Not quite a "son of Faraday" but a Chartered Electrical Engineer.  Will that
do ?

FIRSTLY A WARNING.  If you don't know what you're doing with mains voltages,
better to seek local expert advice than kill yourself.

SECONDLY. I'm not giving you professional advice or specific circuit
designs, just some friendly help from one model engineer to another.

OK ! The NVR switch must have both Live and Neutral connected to it else how
would you expect the poor wee thing to self hold ?  Usually, both the motor
L&N are connected to separate output terminals and the L&N feed connected to
separate input terminals of said NVR Starter.

When you push the "Start" button (Normally open [NO] contact), the coil is
energised and mechanically closes the circuit contacts to the motor.  At the
same time, there is, usually, a separate NO contact of the starter - in
parallel with the start switch - which is operated and this "shorts out" the
"Start" NO contacts so that the coil holds.

The "Stop" switch (normally closed [NC] contacts) is wired in series with
the coil, "Start" contacts and "Hold" contacts.  Consequently, when this is
operated, the coil de-energises and the motor is stopped.  If power is lost
whilst the motor is running, the coil will be de-energised and the NVR will
"do exactly what is says on the tin".  IE  Release.  It can only remake if
the start button is operated - not automatically when power is re-applied.

One thing to check on your starter - pity you don't have the model number
quoted otherwise I might be able to check myself - is that many of these are
designed to work on 3-phase and, consequently, if they contain over-current
coils [OCC], all three of these need to be connected in order that the unit
operates correctly on single-phase.  This is easy to do by connecting the
output of one OCC into the input of another.  One wire to the motor is then
taken from this second OCC's output whilst the input to the first of the
OCC's is, usually, connected to L.  The remaining third OCC input is,
usually, connected to N and its output connected to the motor.

Obviously, you need to check which of the terminals has the start contact,
stop contact, etc, etc, etc, and to do this, you need either a test meter
capable of tracing through the connections on the contactor using a
resistance range ("Ohms range") - ie without anything like mains connected
OR
A circuit diagram of the contactor.  Quite often there is one in the lid of
same.

Failing that, get hold of a copy of Tubal Cains "Model Engineer's Handbook".
This has a wiring diagram in it of an NVR.  The edition I have is actually
incorrect.  I am told, the latest edition of the MEH has been corrected -
but I cannot confirm this.

Pity you live in the "Emerald Isle" and not locally.  Else I might have been
able to "pop round".  If you left me know your E-mail, I could send you some
diagrams as attachments (usual caveats).  It would help to know the
model/type number of the contactor as well.

Regards
Andy

-----Original Message-----
From: modeleng-bounce@xxxxxxxxxxxxx [mailto:modeleng-bounce@xxxxxxxxxxxxx]
On Behalf Of David Everett
Sent: 19 November 2006 06:25
To: modeleng@xxxxxxxxxxxxx
Subject: [modeleng] NVR connections

Hello all you sons of Faraday


I wish to wire a 1ph 220vac 3/4hp induction motor (ex Myford lathe, I
believe) through a NVR
starter (Square D brand).  The motor and switch came as a 'package'.
Needless to say, there are
no instructions with the switch.

I believe that only the Live wire from the mains goes into the contactor
block and the Neutral
goes straight to the motor.  However, when I try this the contactor does not
hold in.

There are a couple of other (unmarked) push-the-wire-in-the-hole type
terminals, which I think
might be used to energise the coils of the contactor.  If this assumption is
correct, are they
both wired into the Live output terminal or where?


All help greatfully received.

Dave - who is trying to come to terms with this new-fangled electricity
stuff.
The Emerald Isle

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