Re: Fuse for 24V Transformer


Serious Machining wrote:
I'm wiring a remote ON/OFF switch for a large room (window mount) air
conditioner which is otherwise accessible only via a 8 foot step
ladder. Historically, everyone has been going to the fuse panel to do
this. I need to use a low-voltage 24VAC control circuit to keep
everyone happy (don't bother to ask me why). The A/C is on a 240 VAC,
20 amp circuit.
.
The 240 VAC to 24 VAC transformer I have is a White-Rogers (Steveco)
90-T40M2 and it will be controlling a Supco DP30242 (W-R 90-244)
contactor. The same fellow who insists on having the 24 VAC control
circuit, also wants the transformer's 240 VAC input to be fused.
.
As the transformer's output is 40 volt-amps (I know, almost but not the
same as Watts), my simple math tells me that if the transformer was
100% efficient, it should only draw a max of 167 mA. In looking at
fuses, I see that Bussman makes all sorts of 5mm x 20mm fuses under 1
amp. I'm considering using 300 mA fast acting fuses as that's what's
readily available from my local Grainger store.
.
Am I on the right track here ? I just hope my 'friend' doesn't insist
that the 24 VAC wiring also be fused. Or should it, just to be
absolutely safe ? The transformer will be installed in a tight
location where there will not really be any air flow to draw off heat.
And it will likely be energized (even with the A/C OFF) all the time,
all year long.

I do quite a bit of work with 24 volt control circuits and I've never
felt the need to fuse the input side of the transformer..... I always
fuse the low voltage side...and usually use transformers with built in
circuit breakers. Transformers for the most part dont just fail....Ive
seen them 50 years old still kicking it....problems usually arise on
the low voltage side in my experience.

.

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