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  1. #1
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    Default Size of supply cable for induction motor?

    Hi,

    I'm fitting a new on/off switch to a small, second-hand drillpress that's powered by an induction motor and would like to confirm the size of supply cable (i.e. how many amps capacity)I should be using to ensure safe operation. The motor specs are as follows; Input voltage 240 volts AC single phase/ Output 370 Watts / Amps 3.90 / Rating Continuous / Insulation class E . Also, there is no starting capacitor that I can see.

    I'm aware that current draw on start-up can be a lot higher than that stated on the motor plate for normal loading - hence the reason for my post.

    Regards
    Swarfman

  2. #2
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    Default

    Simple answer: the kind of wire you would find in an extension cord. It has a rating of 10 Amps or higher - usually!

    More complicated answer: drill presses are usually started in a "no load" condition, and from the motor data you have supplied, the 3.9 Amps would be taking into account the "starting" current.

    Remember on starting not much energy is used by the load - the drill bit.

    A motor with a 240 volt supply, and a rating of 370 Watts, at an assumed Power Factor of 0.8 would draw 1.927 Amps (calculated) from the supply at FULL load. This is about half of the stated 3.9 Amps, so conductors rated at 5 Amps would be suffice, but 5 Amp conductors are not common, so 10 Amp cable would be a bit of "over engineering" but cheaper!

    Hope that makes sense!

  3. #3
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    Talking

    Quote Originally Posted by A J in WA View Post
    Simple answer: the kind of wire you would find in an extension cord. It has a rating of 10 Amps or higher - usually!

    More complicated answer: drill presses are usually started in a "no load" condition, and from the motor data you have supplied, the 3.9 Amps would be taking into account the "starting" current.

    Remember on starting not much energy is used by the load - the drill bit.

    A motor with a 240 volt supply, and a rating of 370 Watts, at an assumed Power Factor of 0.8 would draw 1.927 Amps (calculated) from the supply at FULL load. This is about half of the stated 3.9 Amps, so conductors rated at 5 Amps would be suffice, but 5 Amp conductors are not common, so 10 Amp cable would be a bit of "over engineering" but cheaper!

    Hope that makes sense!
    Hi,

    That's the answer I was hoping for - bits'n'pieces that are easy to source.

    Thanks muchly for taking the time to reply.

  4. #4
    BobL is offline Member: Blue and white apron brigade
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    Quote Originally Posted by Swarfman View Post
    Hi,

    That's the answer I was hoping for - bits'n'pieces that are easy to source.

    Thanks muchly for taking the time to reply.
    A few years back my young bloke worked for an IT company that go all their extension and computer cords tested and tagged but it was cheaper to just buy new cords. He collected up the old cords and gave them to me ie a green garbage bag full of cords. These were typically 10A cords twith a regular 3 pin plug on one end and kettle cord sockets on the other. They make great cords for setting up most 10A or less machinery which I did a lot of at the mens shed. Pity he's left working for that IT company (now works from home) and I have almost run out of cords!

    A few months back I used a 3 core cord without checking to control a small (9.6A) tempering oven and noticed the cord got quite warm over time - when I checked it I saw it was actually rated for 7.5A - I doubt it was even suitable for that current. - never seen one like that before.

  5. #5
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    Basic answer to your query, just in case you were planning to buy new rather than sieve through the junk box, would be 3 core 1.0mm dia flexible cable and a 10 A 3 pin plug, both of which should be readily available from a hardware store. Suggest you work out how long you need the cable to be to function as desired without needing an extension cable, and round up a bit and buy by the metre. You might also want to locate a decent modern cable gland to suit the cable for the entry into the power switch module. A modern gland will provide strain relief for the cable and go a long way to keeping dust and insects away from the switch.

    A junk box cord may not be the way to go unless it has either a conductor size or current rating embossed into the cable sheath at regular intervals. With a lot of cables etc coming from our Chinese friends, many items have underrated cables to supply them. These can be hard to recognize visually as the crafty devils worked out that PVC is way cheaper than copper and often use miniscule conductors with thick individual insulation and thick overall insulation, so they appear outwardly to be a fairly normal 3 core 1mm dia cable, but have a much lower current rating.
    I used to be an engineer, I'm not an engineer any more, but on the really good days I can remember when I was.

  6. #6
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    ....... With a lot of cables etc coming from our Chinese friends, many items have underrated cables to supply them. These can be hard to recognize visually as the crafty devils worked out that PVC is way cheaper than copper ........

    Reminds me of a visit to a friend about ten years ago. He worked for Toolmart or someone like that, and had a "Plugs and Cables" electrical ticket, although he was a gas fitter by trade, and a brilliant welder as well. The back of his ute was full - to overflowing with three pin plugs. All had been cut off the cable at the plug. They looked brand new. Being nosey, I said "Wot's goin' on 'ere now!" The answer was that his employer had imported a container load (or two) of some nice new hand tools. The plugs (plug tops) must be a certain diameter to meet Australian Standards. These imported plugs were about 1mm (or a tad more) too small in diameter, and he, and two other blokes under his supervision had been changing them for about a week, and this ute load was not the first!

  7. #7
    BobL is offline Member: Blue and white apron brigade
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    If you intend purchasing new I found it is usually cheaper to buy an extension cord and cut the socket end off than it is to buy the plug and same rated cable separately.

    Eg at Bunnings:
    HPM 3 core 10A plug costs $6 and 1.0mm/10A cable is about $2/m so a 5m extension costs $16
    A 1.0mm/10A rated extension cord can be had for $7.

    10m 15A cable is about $3/m so just the cable alone costs $30, plug is also about $6
    A 10m 15A extension costs $22.

    A while back Bunnings had 3m 10A extension cords on special for $2 so I bought a dozen of those and used them up at the mens shed.
    BTW I'm not a sparky but all my stuff gets checked out before general use by the shed electrician.

  8. #8
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    Thumbs up

    Hi Swarfman,

    This is what you are looking for ! But there are lots of charts on the web.

    https://www.spwales.com/cable-size-current-rating-chart

    Note that this chart diameters are over the insulation for the individual conductors, and assume British Standards for cables.

    Or this one.

    https://www.reconelectrical.co.uk/im...Capacities.pdf


    Though I do agree with the comments made about Chinese electric cables. Even buying off the roll in in a store, do check the cable conductors cross section or where it is made if you can. The labels on the reel are not always truthful !
    Best Regards:
    Baron J.

  9. #9
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    Default

    Everyone seems to have it covered for you.
    Just to add I've been through this about 12 months ago building my crane needing 10amp cable and others earlier for shed supply etc, the charts are online in pdf from Olex for amp capacities.

    It was cheaper to buy extension cords and cut both ends off, it was that and colour black suited my application (try buying black cable from Bunnings off the roll) yes it is available from eleco suppliers but way more cost than a $5 for a 5m extension lead from ebay delivered to your door from Australia in a well known arlec brand that is sold everywhere here including Kmart.

    Not sure if it matters, but to me back cable looks factory, orange is more a industrial looking cable.
    Again to my eyes a 10amp orange cable in a home shop it looks like you have used extension lead, or it has been replaced.
    Using Tapatalk

  10. #10
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    Quote Originally Posted by BobL View Post
    If you intend purchasing new I found it is usually cheaper to buy an extension cord and cut the socket end off than it is to buy the plug and same rated cable separately.

    Eg at Bunnings:
    HPM 3 core 10A plug costs $6 and 1.0mm/10A cable is about $2/m so a 5m extension costs $16
    A 1.0mm/10A rated extension cord can be had for $7.

    10m 15A cable is about $3/m so just the cable alone costs $30, plug is also about $6
    A 10m 15A extension costs $22.

    A while back Bunnings had 3m 10A extension cords on special for $2 so I bought a dozen of those and used them up at the mens shed.
    BTW I'm not a sparky but all my stuff gets checked out before general use by the shed electrician.
    Kmart has the 5m 10a for $5 in black everyday and free postage over $50 I think it is., I found them on ebay from jaycar delivered for $5.
    I bought a arlec swivel head/plug extension lead from Bunnings for an application, never seen one before, I think it was around $12 for a 3m.
    It will swivel a fair way either side, only downside is they don't make it in black which is what I wanted, lol
    Using Tapatalk

  11. #11
    BobL is offline Member: Blue and white apron brigade
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    Quote Originally Posted by Dave J View Post
    Not sure if it matters, but to me back cable looks factory, orange is more a industrial looking cable.
    Again to my eyes a 10amp orange cable in a home shop it looks like you have used extension lead, or it has been replaced.
    While I prefer black or grey, most of the 3P machines in my shed are on orange cable from a roll. A couple years ago I found a roll of about 20m of of grey 600V 6 core cable in a skip which I have used on a couple of smaller machines. With that cable I also figured it could carry 3P, plus SP and E, through the one cable if I needed to.

  12. #12
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    Default

    Looking at ratings I found out 1 square mm per 10 amps for 240V. 10 amp extension leads often are 1 square mm. 15 amp leads are 1.5 square mm. Of course for long lengths my rule of thumb is out.
    Gold, the colour of choice for the discerning person.

  13. #13
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    Default

    This is from AS3001 for caravans but helpful for extension leads.
    Attached Images Attached Images

  14. #14
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    Default

    Quote Originally Posted by BobL View Post
    If you intend purchasing new I found it is usually cheaper to buy an extension cord and cut the socket end off than it is to buy the plug and same rated cable separately.
    Agreed. Done that many times.
    Chris

  15. #15
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    Default

    [QUOTE=A J in WA;1979367]Simple answer: the kind of wire you would find in an extension cord. It has a rating of 10 Amps or higher - usually!

    More complicated answer: drill presses are usually started in a "no load" condition, and from the motor data you have supplied, the 3.9 Amps would be taking into account the "starting" current.

    Remember on starting not much energy is used by the load - the drill bit.

    A motor with a 240 volt supply, and a rating of 370 Watts, at an assumed Power Factor of 0.8 would draw 1.927 Amps (calculated) from the supply at FULL load. This is about half of the stated 3.9 Amps, so conductors rated at 5 Amps would be suffice, but 5 Amp conductors are not common, so 10 Amp cable would be a bit of "over engineering" but cheaper!

    Hope that makes sense![/QUOT

    Did I read your reply right?
    the motor spec of 3.9amps is the FLA and does not include starting amps. It is the max amps at full load under running conditions.

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