Dust Extractor dimming lights in house


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Established Member
20 Mar 2019
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I recently purchased a second hand Felder AF22 dust extractor with a 4hp motor. I've had some trouble with it tripping the switch but the electrician is coming to fit a C25amp breaker in it today. It currently has a C20amp breaker. Now I have managed to have it running it just wont stay running or sometimes won't start but that all should be fine once the breaker is installed.
However when it is running the lights in the house dim and stay dimmed until it is turned off.
Apart from the annoyance can this cause problems or there something at fault? I am going to ask the electrician this evening but would also like to find out other people's opinion and experiences too.

By the way the extractor has fantastic suction even through the last port of my 6" duct very happy with it otherwise
I would say it is pulling too much power and so starving the rest of the house. I had a similar problem with a milling machine or arc welder; I can't remember which now.
It may require an upgrade to the incoming electrical supply unless you and the wife are happy with the lights dimming.

Depending how efficient the extractor is it will probably be using over 12A and more on start up. In England the standard supply is I think 80A but may be lower where you are.
Felder AF22 only uses 3KW (about 14A) - dimming lights would worry me since an electric oven is about twice that and they don't effect lights unless there is an issue !
Your extractor will be pulling 15 to 20kW for a moment or two while speeding up. That's a lot more than an oven and if your supply is old or cables are feeble, that might well be visible as dimming the lights.
Once up to speed, if the lights aren't back to normal, you could have an issue.
Motors aren't the same as electric heaters. You can't say 3kW / 240v = 13A.
The sparky should look at the motor nameplate and allow for the power factor as well as full load current when deciding what size circuit is required.

He can also test the impedance of the supply at the consumer unit. That will give him an idea of whether your incoming supply cables are adequate or showing signs of age.
The electrician was just here he fitted the new breaker and he measured the voltage on startup and while it was running with the table saw and the voltage was fine. It might of just been that particular night there was a lot on in the house there was no dimming this evening.
Thanks all for your help hopefully it'll be good now
My amplifier receiver dims my lights when I switch it on, so does the hoover, but funnily enough, not the oven. But yes absolutes my table saw when it fires and then again when the dust extractor comes on cause two separate dimmings that stay dim in the house for the duration of use. My workshop is split off supply before the house consumer unit. I've often thought my supply was weak but nothing other than the lights has ever suffered for it. I don't worry about it, just one of those things. I wonder if the lights would still dim if they were all the old 60watt bulbs instead of these 3-7watt energy efficient lights?
Eyes are quite sensitive to quick changes in brightness and filament lamp brightness is also quite sensitive to supply voltage.
Bulbs are quite a good indicator of voltage drop.
There is no way thay anyone can say what is causing this issue because there is insufficient information provided, the reason for the house lights dimming is voltage drop and this is a sure sign of overloading. You cannot just increase the rating of a protective device because it trips, the circuit would have been designed around that rating and increasing it from 20 to 25 amps or changing the curve from a B to a C requires design input. This is like replacing the fuse in a plug top with foil or just wrapping wire around where the fuse should be.

If I was asked to guess at whats wrong I would suggest the supply cable to your workshop or how your workshop is supplied from the domestic property but if you have an electrician coming round then with a few measurements he should get to the bottom of it.

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