Workshop feed

[Sidewinder]

If that's the house end then scrap my Q.

We need a bit more info.

 

[JFC]

What info do you want off the motor plate ? I can see it but getting a picture is a nightmare .

I guess by more info you need to know what machines i have and the start up loads ?

 

[Badger]

we need to know its current rating in amps or itss wattage in watts ie 2.7kw etc

 

[SPECIAL LOCATION]

Im a carpenter and joiner mate . I just do wood stuff and have no idea about electrics . When the electrician turns up on site he normally turns the power off so i go home .

Clearly on a 40m cable working something a bit more juicy than a flymo, a battery charger and a 100w lamp there is a bit of calculation needed around the expected max demand in order to check the right size cable is used...

BUT....

the OP is not an electrician and info is a bit limited....

So lets works things back the other way a bit....

{do it in stages to others can follow the logic if they want to...}

Consider we are designing this external supply not knowing what the max demand is but customer wants to know what he can get for a certain budget....

Appendix 4 of the regs tells us lighting circuits must not drop more then 3% (6.9v)

and other circuits must not drop more than 5% (11.5v)

And assuming we are using a copper cable our volt drop figures mV/A/m can be found for different cable sizes

on page 149 of the OSG.

2.5mm2 has mV/A/m of 18

4.0mm2 has mV/A/m of 11

6.0mm2 has mV/A/m of 7.3

10.0mm2 has mV/A/m of 4.4

So if looking a max allowable current /power @ 5% volt drop over 40m run.

2.5mm2 can run 15.9A or 3.7kW

4.0mm2 can run 26A or 6.0kW

6.0mm2 can run 39A or 9.0kW

10.0mm2 can run 65A or 3.7kW

But if we have to satisfy the 3% rule....

those numbers reduce to...

2.5mm2 can run 9.6A or 2.2kW

4.0mm2 can run 15.7A or 3.6kW

6.0mm2 can run 23.6A or 5.4kW

10.0mm2 can run 39A or 9.0kW

Others can work out larger sizes if they want..

but surely a 16mm on a domestic outbuilding is getting a bit industrial????

any help????

:C :coffee

 

[JFC]

PL Amps 16.4

Is that what you need ?

The table saw is 16 and the tenoner is 13.4 but has two motors so double that .

Do you need all the machines ? That could take a while :^O

I should add that these machines are normally three phase and the single phase ones i have where a special order from Wadkin .

 

[kme]

IF we presume that you`ll only run 1 machine at a time......then the heaviest load is the one we want.

PLUS any smaller loads (lighting, etc) that will be on at the same time.

So if we go with 16.4; and *assume* that you`ve another 10A of load (lighting; and maybe a heater when its cold?)

We can easily see from SpecLoc`s post above that we`ll need at a minimum 6mm cable. Your existing 2.5mm could hold almost 16A; but that isn`t enough for the running current; let alone startup, to overcome inertia etc.

4mm might be sufficient; but why work so close to your maximum. Allow some "headroom" in the design. If I was installing for you from scratch; I`d probably try to convince you to put 10mm in, TBH.

KME

 

[Sidewinder]

The BAOS has a 3hp motor, trust me, I have one in the back of the van that's goosed!

I can get all the rating plate details off it later, but it is the 3ph version.

 

[apprentice87]

Hi All,

A 3hp single phase motor is going to draw quite a wacking current at start up.. I think it is about 7 to 10 times FLC....

john...

 

[JFC]

The BAOS has a 3hp motor, trust me, I have one in the back of the van that's goosed! I can get all the rating plate details off it later, but it is the 3ph version.

 

[roys]

Could you go back to using a 3 HP, 3 Phase motor with a single phase to 3 phase inverter so you could 'soft start' it say over 4 seconds and as the inverter will probably use PWM it will limit the start current as I understand it. Of course I know we are talking more cash here and moving away from the original OP question, but it is late and I am thinking out loud.

 

[JFC]

Could you go back to using a 3 HP, 3 Phase motor with a single phase to 3 phase inverter so you could 'soft start' it say over 4 seconds and as the inverter will probably use PWM it will limit the start current as I understand it. Of course I know we are talking more cash here and moving away from the original OP question, but it is late and I am thinking out loud.

I would still need to upgrade the supply to do that though woudnt i ?

Aswell as find a new motor , buy a converter and turn the BAOs upside down again ray

 

[roys]

Hi JFC

By the sound of things what ever you do, you do need to upgrade your supply, I had a similar install, 40 meter run to garage / workshop and I had a 3 Phase 3HP 1966 Colchester Master lathe to power up as well as other kit, I did the sums and it came out to 10 mm cable, the 40meter gets you on that pesky Volts Drop .

As a by the way, I originally had a rotary converter giving me the 3 phase for my lathe but I have just bought an inverter to do the job. The rotary converter was using 10 Amps before I had even switched the lathe on.

 

[apprentice87]

Hi JFC

Why not just get a proper three phase supply, it might be a LOT cheaper than you think....

john...

 

[JFC]

Because i dont have any three phase machines .

 

[apprentice87]

Ah, forgot about that!! Still, you could always get a three phase supply, but just split up the phases, so you would in effect have three times what you have now, and add to the value of you house and workshop at the same time!!

john..

 

[Evans Electric]

Just my input at this stage , factor in the point that its a one man operation , one machine working at a time plus your extraction , lights and heating I guess. Should keep your cable size down a bit .

Bit like some work we did once for a well known chairlift firm. Our young sparky wanted to fit a 3way C/U and 3 circuits to 3 spurs feeding stairlift, hoist on landing and hoist over bed.

For some reason he thought I was rough in just looping the 3 spurs together on a radial. :C

 

[JFC]

I had an electrician mate take the motor away to be fixed but he has done his back in ( probably lifting the motor ) He is the person that said the feed needs to be upgraded and the reason for me asking here in the first place . I didnt understand why before but i think ive got the idea now .

He said he was going to do the calculations and let me know what i need to buy . He mentioned 10 maybe 16 but this was a few weeks ago and he still hasnt got back to me ( still off work with his back )

I got some prices for 10mm and 16mm armoured cable and there was about

 

[apprentice87]

Hi There,

For the price difference i too would have the 16mm...As to the type of cable, we would need to know what type of earthing arrangements you have in the house. Post a photo and we will be able to tell you!!

Do you intend to run the cable underground or fixed to a wall or whatever??

john...

 

[JFC]

It would have to be surface run so i guess in some form of pipe if thats needed ?

This is the house end .

 

[m4tty]

Armoured cable aka swa doesn't need to be enclosed. It's fine to run it surface mate. I'd run it past your sparky first for cable route as he will be signing it off