Switch rating - what does 3(1)A mean?

[Michael Chare]

If a switch is rated as 220/240Vac, 50/60 Hz 3(1)A

What does 3(1)A mean and is this a standard nomenclature?

Michael Chare

[stefek.zaba]

Probably, the 3A rating is for a "nice", resistive load, such as light blubs, while the derated 1A rating is for a "nastier" load, such as flourescent lamps, transformers, and other things which are likely to produce more of a spark/arc as you interrupt the supply.

Stefek

[Harry Bloomfield]

On 11/01/2004 Michael Chare opined:-

3amp will be the resistive load rating and 1amp the inductive load rating.

[Dave Liquorice]

It can switch 3A with a resistive load or 1A with a reactive load.

[Lurch]

3 amps resistive, (heating elements, lightbulbs etc..). 1 amp inductive, (flourescent lights, motors etc..).

[Michael Chare]

Thanks for all the replies.

I have just bought a Danfoss-Randall TP9 Programmable Room Thermostat + H/W Timer.

Although I downloaded the installation instructions before buying it, I failed to notice that it is only rated at 3(1)A.

There is no label on my boiler to show the power consumption. All the boiler instructions say is fit a 5A fuse, I changed this for a 3A fuse to match the programmer. So far this has not blown.

I got out my multimeter. In round numbers the boiler draws 1.75A at for the first 8 seconds when it starts (when the igniters are working) and 0.75A there after when only the motor that drives the fan and oil pump is running. The central heating water pump draws 0.25A.

The TP9 uses separate relays for the boiler and water pump.

My multimeter has a facility for recording peaks, but I suspect that this picks up switching transients rather than any additional current that the motor might draw at start-up.

Michael Chare

[Lurch]

[..]

Wouldn't worry, you're unnecessarily worrying yourself, it's designed to switch boilers on and off, fit it, stick a 3amp fuse in the spur, that's it. I've never come across an overloaded room stat or programmer yet!

SJW

[Dave Liquorice]

Gas boilers take very little power(*) compared to a oil boiler. The OP mentions 8 seconds and ignitors I'd take that to mean he has an oil boiler...

(*)Though the fan flued jobbies will take more than a normal open or balanced flued thing where the only load is the gas valve. I still doubt it matches the blower/high pressure pump of a oil boiler.