Can anyone explain electricity, watts and such to me?

[Scouse]

I've just ordered my first woodworking machine, a Jet bandsaw from Axminster, but the electric thing is confusing me as follows;

It's listed as having a 1.1 KW power rating with a 1.9 KW max. input. The catalogue also recommend a 16 amp supply.

My question is this; my mother's Flymo has a 1.8 KW motor and my wife's hairdryer has 2KW printed on a label on the side, neither of which need a big blue plug, so why would a machine with the above specs and a seemingly lower power rating require such a thing?

El.

 

[tekno.mage]

Because of the in rush (start up) surge. Big machines like bandsaws and workshop dust extractors use large powerful motors and draw very high start-up currents for a short time when first switched on - which is why the 16A supply is recommended - anything lower risks blowing the fuse when you start the machine. The power ratings given are for continuous power - so the bandsaw probably uses 1.1kW when running, but may well draw a lot more than that momentarily when switched on.

Your other domestic equipment may well have a higher continuous power rating (well within the rating of a 13Amp socket in fact) but don't have a large start up surge. Also most of the 2KW power rating for the hairdrier will be the heating element, not the tiny motor in it. Heating elements don't have high start up surges. The flymo will have a different type of motor (a lot lighter in weight for a start!) in it than the bandsaw and again, will not have big start up surge.

 

[RogerP]

There was a post a few years ago on this topic.

https://www.ukworkshop.co.uk/forums/how-can-i-tell-if-i-might-need-a-16-amp-supply-t22983.html

May be of help.

 

[newt]

Because of the in rush (start up) surge. Big machines like bandsaws and workshop dust extractors use large powerful motors and draw very high start-up currents for a short time when first switched on - which is why the 16A supply is recommended - anything lower risks blowing the fuse when you start the machine. The power ratings given are for continuous power - so the bandsaw probably uses 1.1kW when running, but may well draw a lot more than that momentarily when switched on.

Your other domestic equipment may well have a higher continuous power rating (well within the rating of a 13Amp socket in fact) but don't have a large start up surge. Also most of the 2KW power rating for the hairdrier will be the heating element, not the tiny motor in it. Heating elements don't have high start up surges. The flymo will have a different type of motor (a lot lighter in weight for a start!) in it than the bandsaw and again, will not have big start up surge.

+1 comprehensive reply.

 

[The Wood Butcher]

A 13 amp socket is rated to 3200 watts, the 20 amp ring that a 13 amp socket is usually connected to is rated to 4800 watts at 240 volts. These are nominal ratings as the EU says leccky should be 230v, for presumably unknowable EU-type reasons (free movement of domestic electric supplies across borders..?), but since there is a +-10% tolerance most suppliers in the UK still supply nominal 240v...

Anyhow, the trick is to have a slow-trip MCB, which is known as a type-C MCB. These are rated to 5-10 times the nominal rating, and if you run a spur to your workshop using modern cable and fittings this would be fine. However if you are running a spur, you might as well run a 16 amp spur... What causes the high startup surge is a large capacity induction motor turning a large lump of cast iron. Once the lump of cast iron is up to speed, it's momentum reduces the amount of energy required to maintain the operating speed of the motor. If your shiny new bandsaw does have a maximum draw of 1.9kw then you are well within the limits for a standard 13 amp plug

As a quick disclaimer, this is electrical advice and information being given more or less anonymously on t'internet and has as much worth as that suggests. I have managed to cut through two cables that I myself installed, one of which was 3 phase and connected to an uninterruptible power supply so if I wasn't using 10 kv insulated tools I'd probably still be twitching, and I apparently am considered a competent person in the eyes of the law... Go figure... Get a qualified, or even better a competent, spark to check. Those two things aren't always the same. You can measure the amount of current drawn on startup with a simple amp meter.

Edited for stupidity...

 

[Scouse]

Thanks for the replies chaps.

If you don't mind another question, if the motor is rated at 1.1 Kilowatts what is the 1.9 Kilowatt rating related to?

Here's a link to the saw with the specs at the bottom of the page http://www.axminster.co.uk/jet-jet-jwbs ... rod576903/

 

[newt]

Thanks for the replies chaps.

If you don't mind another question, if the motor is rated at 1.1 Kilowatts what is the 1.9 Kilowatt rating related to?

Here's a link to the saw with the specs at the bottom of the page http://www.axminster.co.uk/jet-jet-jwbs ... rod576903/

Read Kym,s reply again particularly the mention of surge.

 

[Jake]

In reality, it will most likely be fine on a 13A plug if the circuit the socket is on is half-way decent. If it works, it works. I run 3hp and 3kw motors on 13A plugs. Axminster are covering their butts so people cannot complain if they need to install a replacement for the long wet string feeding their shed and/or it is just a default warning for any machine.

 

[Lons]

slow-trip MCB, which is known as a type-B MCB

Hi wood butcher

Are you sure that's correct or is it a typo? :?

My understanding is that type B are used in normal domestic circuits and it's type C which are used for initial surge capacity.

I'm no leccy so could be wrong

Bob

 

[The Wood Butcher]

slow-trip MCB, which is known as a type-B MCB

Hi wood butcher

Are you sure that's correct or is it a typo? :?

My understanding is that type B are used in normal domestic circuits and it's type C which are used for initial surge capacity.

I'm no leccy so could be wrong

Bob

You're clearly a better one than I am... This is why no-one should take electrical advice over the internet... Original post edited so as not to confuse the unwary

Yes, type C are the kind that are used for most small machines, with a trip at 5 - 10 times nominal rating, and there is also type D that trip at 10 - 20 times nominal.

 

[The Wood Butcher]

In reality, it will most likely be fine on a 13A plug if the circuit the socket is on is half-way decent. If it works, it works. I run 3hp and 3kw motors on 13A plugs. Axminster are covering their butts so people cannot complain if they need to install a replacement for the long wet string feeding their shed and/or it is just a default warning for any machine.

Absolutely the case. We run 3kw lamps off domestic sockets on location, but they have very little startup surge

 

[Lons]

slow-trip MCB, which is known as a type-B MCB

Hi wood butcher

Are you sure that's correct or is it a typo? :?

My understanding is that type B are used in normal domestic circuits and it's type C which are used for initial surge capacity.

I'm no leccy so could be wrong

Bob

You're clearly a better one than I am... This is why no-one should take electrical advice over the internet... Original post edited so as not to confuse the unwary

Yes, type C are the kind that are used for most small machines, with a trip at 5 - 10 times nominal rating, and there is also type D that trip at 10 - 20 times nominal.

Oh no I'm not :lol:

I'm just a builder and part time woodworker. It's one of those things just stuck in the back of my brain. Only know 'cos I was going to use one for my Sip 10" table saw and Robland planer but decided it was just as easy to stick in a dedicated 16amp supply.

Bob

 

[marcus]

I used to have a bandsaw which just about ran off a 13 amp supply, though it recommended 16 amps. It would usually be fine but it tripped just often enough to p**s me off. I've generally found that when they say 16 amps they do really need it — it's hardly a selling point to make this a requirement if it's not necessary. But by all means try it on the 13 and see, you may be lucky.....

 

[Hudson Carpentry]

I run my axi 10" ts (basically is a sip 10") on a 13amp plug. I have a type c 32amp breaker on the circuit the machines are running on. The table saw which comes with the same 16amp recommendation has never tripped the circuit. I have tripped it by turning the p/t and exstractor on at the same time. It's fine if I wait a second or two but is a great example of startup currents.

 

[Halo Jones]

In the new year I am going to be feeding a consumer unit in the workshop from a spare way on my main consumer unit in the house. From the discussions above do I want a B or C type MCB in the main consumer unit in the house or is it OK to have the C type only in the workshop?

 

[The Wood Butcher]

In the new year I am going to be feeding a consumer unit in the workshop from a spare way on my main consumer unit in the house. From the discussions above do I want a B or C type MCB in the main consumer unit in the house or is it OK to have the C type only in the workshop?

Depends on the rating of the spur to the workshop. For instance, I have a 32 amp MCB in the consumer unit in the house for the circuit to the workshop, with the appropriate wire to the consumer unit in the workshop. Remember that the fuse protects the wiring and prevents it from overheating, it's not there to protect what's plugged into the circuit... In the workshop I have a 16 amp circuit to run my machines from. It has a type C MCB. The consumer unit in the house has a type B MCB as nothing I'll plug in will get anywhere near it's limit, and so it doesn't trip, as the limit of a 32 amp type B is 150 amps, give or take. Since the feed to a house is 100 amps, it's fine.

 

[Tony Spear]

Thanks for the replies chaps.

If you don't mind another question, if the motor is rated at 1.1 Kilowatts what is the 1.9 Kilowatt rating related to?

1.9 kW in, 1.1 kW out. i.e 58% efficiency (pretty poor IMO).

 

[Jake]

I used to have a bandsaw which just about ran off a 13 amp supply, though it recommended 16 amps. It would usually be fine but it tripped just often enough to p**s me off. I've generally found that when they say 16 amps they do really need it — it's hardly a selling point to make this a requirement if it's not necessary. But by all means try it on the 13 and see, you may be lucky.....

It will depend quite a bit on your wiring and the motor in question. A long cable run before the socket will compound problems considerably especially if it is undersized. They aren't trying to sell on it requiring 16A, but what they are trying to do is avoid come-back when it doesn't work on 13A. Nothing wrong with that, but that does not mean that you should assume that you need a new circuit just because they are telling you in some circumstances you might. The OP's saw doesn't have the biggest of single-phase motors.

He should indeed try it out on an existing circuit. I would, and that's just to save being bothered to do an hour's wiring. The insistence that he needs a 16A circuit could cost him quite a lot of money if he calls someone in. Let him try it. This thread is full of anecdotes which may well not apply (because they often do not, and because the OPs motor is not the biggest that it could be).

 

[Jacob]

I shouldn't tell you this but if 16 amp is required only at start up (as is often the case) you can cheat by sticking a bit of 5 amp fuse wire alongside your 13 amp fuse to crank it up to 18 amp in theory. Most of the time it will be running safely at well under 13 amp. The circuit itself will be protected by a 20 or 30 amp fuse anyway.
I found this out when I bought an Axi 2200 dust extractor. They were a bit vague about the 16 amps. Later models had better motors demanded less current at start up.

 

[CHJ]

..If you don't mind another question, if the motor is rated at 1.1 Kilowatts what is the 1.9 Kilowatt rating related to?
..

Efficiency rating.

Power IN is greater than power OUT due to the energy lost in turning the motor itself.