Linisher cuts out, what to do…?

[Les Jones 1Participant @lesjones1]

I think even a 16 amp supply is being veru optamistic. Altough a 3KW RESISTIVE load takes 12.5 amps at 240 volts an induction motor will have a poor power factor so although it will take 3 KW of power it will take more than 3 KVA. Here is a link to a web page that show the full load current for single phase induction motors. This link shows the full load current for a 3 KW motor to be 22 amps The starting current will be even higher.

Les.

[Brian Sweeting 2Participant @briansweeting2]

An approximate inrush current for that size motor would be 40 odd amperes so I'm not surprised that the little 24amp fuse keeps blowing.

A proper overload and mcb need fitting.

Mind you, it could have a faulty starting capacitor and we're all barking up the wrong tree.

[not done it yetParticipant @notdoneityet]

I would nor even be trying to run a 4

HP motor from a 13 plug top. Probably not, even if soft start. By the way, the fuse is there to protect the lead. Overloads are what you need to protect the motor.

[Brian Sweeting 2Participant @briansweeting2]

Sorry, just reread my post above, should of course read "13amp" not 24.

[Richard Harris 5Participant @richardharris5]

Does anyone have an idea as to what type of rcbo (what amp rating) would be needed for this? My dad has a spare / new fusebox that he seems to be fitting this morning in the outbuilding.

[clogsParticipant @clogs]

Funny how one job leads to another !!!!!!!!

I think u should get a direct suppy to the shed with it's own fuse board…

u'll never look back once done……not nec, that expensive for a single phse supply…….

good luck, clogs

[Frances IoMParticipant @francesiom58905]

I think you would be better advised to get some professional advice – eg as to what cabling is required to the outbuilding, what type of connection is required at your house + outbuilding fuseboxes etc – I don’t know what insurance policy you have but suspect if any fire caused by inadequate/incorrect wiring etc will all too readily be used by the company to reduce payment

[Richard Harris 5Participant @richardharris5]

Posted by Les Jones 1 on 26/08/2017 20:05:36:

I think even a 16 amp supply is being veru optamistic. Altough a 3KW RESISTIVE load takes 12.5 amps at 240 volts an induction motor will have a poor power factor so although it will take 3 KW of power it will take more than 3 KVA. Here is a link to a web page that show the full load current for single phase induction motors. This link shows the full load current for a 3 KW motor to be 22 amps The starting current will be even higher.

Les.

Thanks Les. I did find this PDF (link below) which shows similarly, a 3KW motor needs a 25AMP fuse and a 35AMP circuit breaker. I understand axminster recommend an electrician do this, but also, I don't see what it doesn't give such info in the manual…

https://www.google.co.uk/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=0ahUKEwia9uHbhvfVAhUsLcAKHRiWBYEQFggmMAA&url=http%3A%2F%2Fgroverelectric.com%2Fassets%2Fdownloads%2Fhowto%2F20_How%2520to%2520Calculate%2520Wire%2520%26%2520Fuse%2520Sizes%2520for%2520Electric%2520Motors.pdf&usg=AFQjCNG8eBEoyy-GZbuL3x0cOOwYzy0b4g

[Richard Harris 5Participant @richardharris5]

Posted by clogs on 27/08/2017 09:25:47:

Funny how one job leads to another !!!!!!!!

I think u should get a direct suppy to the shed with it's own fuse board…

u'll never look back once done……not nec, that expensive for a single phse supply…….

good luck, clogs

Hah! So true… painfully true. Like wanting to make an apple pie and then suddenly you own an orchard…

Yeah we are going to do this, my dad had a brand new fuse board for something else (my sister needed one for their new house, but used something else in the end). I think when we have this in it'll make it much easier for all the tools in their… including setting up an appropriate circuit breaker for the linisher.

[Richard Harris 5Participant @richardharris5]

Posted by Frances IoM on 27/08/2017 09:50:21:
I think you would be better advised to get some professional advice – eg as to what cabling is required to the outbuilding, what type of connection is required at your house + outbuilding fuseboxes etc – I don't know what insurance policy you have but suspect if any fire caused by inadequate/incorrect wiring etc will all too readily be used by the company to reduce payment

Good point. I have suggested this twice already (getting the electrician in), and it's been pushed back. I'm only here for a few more days so will have to work harder with my campaign .

Appreciate all the advice people. I did try to quote and thank you all earlier but was on my phone, and that feature doesn't work.

Thank you for the help!

[Richard Harris 5Participant @richardharris5]

Good news: he's contacting the electrician he knows well tomorrow evening. Bad news: an oak bowl just exploded on is lathe and hit him on the head and shoulder. Not ideal!

[Brian Sweeting 2Participant @briansweeting2]

Remember that you want a motor rated MCB fitted.

[Richard Harris 5Participant @richardharris5]

Posted by Brian Ess on 27/08/2017 18:36:02:

Remember that you want a motor rated MCB fitted.

I would be assuming the electrician would know this…? Should I have to tell him? If so, how am I meant to know what MCB to tell him to fit? Isn't that his job!?

IIRC, he's had contracts working on installing machinery at a local MOD, so he will hopefully know what he's doing. Hopefully.

Unfortunately, he can't come for a few days, and I'm leaving here tomorrow so will probably be another month until I get to have a play with it

[Brian Sweeting 2Participant @briansweeting2]

Richard, agreed your electrician should be aware of the requirements but a "domestic" might not 'naturally' think about that side of things.

A type C is the minimum needed.

**LINK**

[Richard Harris 5Participant @richardharris5]

Thanks Brian, it's a good point. I'll make sure I bring this up or have ti written down for him.

Axminster got back to me today. Their official recommendation is:

The 240v model needs a 16amp supply so a 16amp workshop socket run through a 16amp C typr MCB in the consumer unit.

**LINK**

I did double check with him that 16amp MCB would be sufficient, and they seem to think so…

[Brian Sweeting 2Participant @briansweeting2]

It's one of those things I think as we, non-electrical types, confuse ourselves with is that fuses are there to protect the cable not the item on the end if the cable.

With smaller loads such as table lamps or computers we follow recommendations and perhaps fit 3 or 5 amp fuses on a cable that could support a 13amp load.

In the case of motors etc the high current inrush at the start is of such a short duration that the cable can absorb the over current but a 'standard' fuse/mcb cannot.

Anyway, glad to hear/read that Axminster have clarified to unit requirements.

[duncan webster 1Participant @duncanwebster1]

According to **LINK**

a 3kW 220v single phase motor will draw 24A. This doesnt sound unreasonabe when you take efficiency and power factor into consideration. If you're running off a 16A MCB don't push too hard.

[JasonBModerator @jasonb]

I would think the motor runs at 2900rpm so will draw less current than the 1450rpm ones in Duncans link.

Quick look at the parts diagram and it is direct drive off the motor, belt speed of 29m/s which works out quite nicely to 2900 reves on a drum just under 200mm dia. which looks about right size wise

[Richard Harris 5Participant @richardharris5]

Posted by duncan webster on 29/08/2017 17:36:14:

According to **LINK**

a 3kW 220v single phase motor will draw 24A. This doesnt sound unreasonabe when you take efficiency and power factor into consideration. If you're running off a 16A MCB don't push too hard.

Thanks Duncan. We'd found similar info as well, which is confusing. Axminster say 16amp will be fine though. I've written the info down for the electrician so hopefully he'll be able to work it out and make an educated guess…

[SillyOldDufferModerator @sillyoldduffer]

Posted by Richard Harris 5 on 30/08/2017 09:29:16:

Posted by duncan webster on 29/08/2017 17:36:14:

According to **LINK**

a 3kW 220v single phase motor will draw 24A. This doesnt sound unreasonabe when you take efficiency and power factor into consideration. If you're running off a 16A MCB don't push too hard.

Thanks Duncan. We'd found similar info as well, which is confusing….

It is very confusing, which is why an electrician may be needed. As I understand it:

1. A unusually heavy pulse of current is drawn briefly when a single phase motor is started. On a 3kW motor, the start current could well be enough to blow a 13A fuse.
2. Once the motor is spinning, the current falls dramatically. Off load, i.e just turning the belt on a linisher, perhaps an amp or two. So if the13A fuse survived switching-on, the motor works.
3. But the current drawn by the motor rises as soon as the motor is asked to do work. The 3kW rating is the maximum amouint of work the linisher motor should be asked to do. Anyway, 3kW at 240V is 12.5A, which while not unacceptable through a 13A fuse, is close to the limit.
4. If you overload a motor it will draw more than the rated current. You need a fuse to blow rather than have the motor burn out, or damage the supply wiring. Replacing a fuse with a paper-clip is never a good idea!
5. Calculating the current drawn by an AC motor is more complicated than it is for a DC motor. My 3kW = 12.5A is an approximation, which matters when the load is already close to the edge.
6. Also, depending on the small print, the kW rating of a motor may refer to either input or output. If it's 3kW output, then the current draw will be about 10% higher than expected. Again this matters if the circuit is close to the edge.

A 3kW motor on domestic electrics is an awkward beast. On the face of it, it might work OK on a 13A plug. Quite likely it won't! It straddles the line between 'just plug it in' and 'fit proper electrics'.

Though I can think of a bodge, I'd pay to have the wiring done properlty. That is a dedicated line with a motor rated circuit breaker. The latter tolerates the short burst of current at switch-on and disconnects properly if something goes wrong. The dedicated line part is well within the remit of a domestic electrician (electric showers and cookers). I've no idea if their training includes motor-rated circuit breakers and would mention it just in case.

Dave

[Richard Harris 5Participant @richardharris5]

Thanks for breaking that down for us! That is my understanding as well, based on what you guys have said, and some other research, and Axminster. We do have an electrician appearing at some point (not exactly sure when) but he's always been super knowledgable in the past, so I am very hopeful he'll be able to handle this.

About load and amperes though, I hadn't thought this through fully until you wrote it down.

My dad has his woodturning lathe in there, and although the torque setting is set correctly, it does sometimes slow or even cut out at times on very hard, dry wood (even with a freshly sharpened tool). I wonder if this could relate to the same issue? Not having the correct power supply? Although, it is more complicated, as it's 3 phase with a converter.

[not done it yetParticipant @notdoneityet]

Another 'factor' might be Cos θ. These electric motors have a lousy power factor, even at the best of times. I don't know how that might affect things at start up – certainly almost resistive before the motor turns. 3kW is 3.75kVA @ COS θ of 0.8 (probable normal running situation).

Anyone care to enlighten?

[Richard Harris 5Participant @richardharris5]

Just to update… a couple of weeks ago I spent an afternoon digging a trench from the house to the outbuilding! Yeah, no sanding happening yet! The electrician is doing pretty much what everyone in this thread said. We need a more heavy duty cable running to the outbuilding, and he's putting a consumer unit in there, along with the appropriate MCB. From what I hear, he's doing it next weekend. He's been very busy so there hasn't been any work done yet, but I don't believe it'll take him long (as he's someone we trust, so we're happy to wait).

It'll be well worth it. It'll improve the whole setup in there, never mind just this beastly linisher.

[Brian Sweeting 2Participant @briansweeting2]

Good news, just make sure that there is a spare 13amp switched socket outlet for the tea kettle.

[Clive FosterParticipant @clivefoster55965]

I had two consumer units put in my workshop. One with the appropriate RCD and MCB fitments for fixed machine tools with larger electric motors and one with a more normal set-up to several ordinary 13 amp rings. Instead of ordinary wall mount sockets I used 8 way metal clad extension boards for the rings. Two boards per ring. Which I happened to have. Definite overkill socket wise for the workshop but it meant I was able to put banks of sockets reasonably close to where i was likely to be using hand held power tools with no temptation to use socket doublers or trailing extension leads.

If using hand held electric tools I figure each tool should be on an individual switch and all the cables should run forward from your working position so you can see where they are. Obviously sometime you have to go round the other side of the job so sometimes cables end up behind but normally in front is best.

Also had couple of weather proof sockets outside for shredder et al. With a nice lever operated disconnector over the door so I can see they are off except when needed.

Clive

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