Tablesaw Choice - Perspective required.

[RogerS]

Jake = 2.5mm seems to ring a bell, mostly probably right. Tomorrow I think i'll post up some pics just to be on the safe side.

BB - just don't get worried if the lights dim on start-up.

 

[Sawdust]

Jake = 2.5mm seems to ring a bell, mostly probably right. Tomorrow I think i'll post up some pics just to be on the safe side.

BB - just don't get worried if the lights dim on start-up.

BB - If 2.5mm is your ring main with a separate circuit for lights and a thicker (6 or 10mm) cable from your house consumer unit to your shed consumer then you will be OK.

If it's a single core 2.5mm supplying everything then I would be careful about buying anything with a big motor.

I'd check first!

Mike

 

[ByronBlack]

The cable from the house to the workshop consumer unit is definitly not 2.5mm, it's a lot thicker. I've not measured it yet, but I would guess it's at least 8-10mm. The 2.5mm cable is what the lighting circuit and the sockets are wired up with inside the workshop. I spoke to my father-in-law last night and he assures me like some of you have that it shouldn't be a problem to run the saw and an extractor. So, I just have to wait until monday and see whats what My incra and extractor should be arriving today though - fingers crossed that Rutlands don't bugger me about!

 

[Jake]

If the SWA is thicker than 2.5mm2 (conductor size), then it can almost certainly run off a bigger MCB than 20A, so it is well worth checking out - the MCB can be changed very easily, unlike the cable.

It's an odd set-up if so as there can't be any discrimination between the main CU and your workshop CU - what rating are the MCBs in the workshop CU?

Are you sure, then, that it isn't a 40A MCB in the house CU (which would imply 6mm2 cable)?

 

[RogerS]

If the SWA is thicker than 2.5mm2 (conductor size), then it can almost certainly run off a bigger MCB than 20A,

Not strictly true, Jake. The rating of the MCB is dictated by the overall resistance of the phase conductor and protective conductor...which in turn is determined by the cross-sectional area of the cable, the length and whether or not any derating needs to be applied to the calculations.

 

[Jake]

Yes, I know. That's why I said 'almost certainly' rather than 'certainly'...

I suppose it could be 4mm SWA with derating factors, but that's a long way from BB's 8mm-10mm guess.

We need some facts, really.

 

[ByronBlack]

fella's, you need to treat my like a small child when it comes to electrics - SWA and MCB mean very little to me, if you can put it in laymans terms, I can probably then go and check and give some definite facts. Although saying that, I think an MCB is the 'trip' switch inside the Consumer Unit?? If so, I have two of them in there, but off-hand can't remember what they are rated at.

The distance from the house CU to the workshop CU is about 15m if that is a factor?

 

[Jake]

fella's, you need to treat my like a small child when it comes to electrics

Don't put your fingers in the sockets, you silly boy.

 

[Jake]

Seriously, your FIL is probably the best source of info, as he'll know what he put in and why.

 

[ByronBlack]

fella's, you need to treat my like a small child when it comes to electrics

Don't put your fingers in the sockets, you silly boy.

Cheers, I'll write that on the back of my hands

You are right of course, my 'FIL' does know the setup, and assures me it'll be fine, but I guess I just always err on the side of caution when I spend a lot of money on a bit of machinery. Either way, the saw is ordered, and I will see whats what on monday

Rutlands have finally pulled their finger out, and I got my incra today. Very impressed with it, it feels nice and solid, the flip-stop is nice and a 31" capacity is great, it's much more better made and heavy duty than it looks in the pictures.

 

[Jake]

Suck it and see, it all got rather OT, really. 20A should be more than enough, and if not one of the MCBs should pop to protect the wiring. The saw will be fine.

 

[Digit]

BB, if you have 2.5 mm cable from the consumer unit your 20amp rating will be about its limit. Convert to a ring main as the easiest way of up grading.
This means that the cable is wired to a socket and then passes onto the next socket. In other words there are 6 conductors in the rear of each socket. When you have wired in the last of your desired sockets the cable continues on back to the consumer unit, (CU) where the three conductors are wired in to the same holes that the original cable is connected to. Hence ring!
This means that 2 2.5mm conductors are now feeding your sockets and doubles the load you may draw, (all other things being equal).
An MCB is a Minature Circuit Breaker, if you look in your CU they have little lever switches on the front, if this is not so then you have either re-wirable fuses, (fuse wire) or cartridge fuses. Either way you can now replace what ever form you have with a 30 or 32 amp MCB and run saw, extractor and coffee maker all at the same time!

 

[ByronBlack]

Digit, thank you for the information and explanations, I'll check out the wiring and see what it is, although I think it might be a ring main as the sockets are wired together as you mention. I definitely have MCB's in my CU. There are two of them, I'm assuming one is for the lighting and the other is for the sockets.

 

[Jake]

The number of wires in (all but one of) the sockets doesn't tell you whether it is a ring (i.e. a loop where the wire comes from the CU, goes through each socket, and then back to the CU) or a radial wired sequentially (i.e. the wire comes from the CU, goes through each socket, but just stops at the last socket instead of going back to the CU). The sockets on a radial circuit can be wired in exactly the same way as in a ring (i.e. with a wire in, and a wire out), except that at the end of the chain, there will not be a wire out back to the CU. So most sockets will look exactly the same either way the circuit is wired - apart from the last one in the chain.

Secondly, there is no reason why your socket circuit cannot be a ring circuit, from the workshop CU, while the main feed from house CU to your workshop CU is a radial (one wire) - in fact, that is the norm and the right way to do it.

It is the main supply from your house CU to the workshop CU which has the 20A MCB on it, and it is that circuit which is the limiting factor. If the 20A MCB is there because it needs to be there to protect the armoured cable to the shed, the proper way to do it is to see if it does serve your needs, and if not, replace the armoured cable with a bigger (single) cable.

Given the expense, let's hope the 20A circuit will be enough (as, in all probability, it will be).

Turn the fan heaters off while you are sawing!

 

[Digit]

BB, I Googled 'Ring Main', it's all there my friend.
Unless you have a lot of lighting the MCB for the lights would be 5 to 10 amp. If it's a ring main the MCB with 2.5 cable would likely be 30 to 32amp.

 

[andycktm]

It's amazing what imformation the "ordinary " person can get their hand's on off the web

 

[ByronBlack]

The number of wires in (all but one of) the sockets doesn't tell you whether it is a ring (i.e. a loop where the wire comes from the CU, goes through each socket, and then back to the CU) or a radial wired sequentially (i.e. the wire comes from the CU, goes through each socket, but just stops at the last socket instead of going back to the CU). The sockets on a radial circuit can be wired in exactly the same way as in a ring (i.e. with a wire in, and a wire out), except that at the end of the chain, there will not be a wire out back to the CU. So most sockets will look exactly the same either way the circuit is wired - apart from the last one in the chain.

Fair enough, I'll look more closely - I know it's probably not needed as I'm almost sure it'll be fine, but I am now quite interested to see exactly how it's all setup (FIL isn't always forthcoming with info).

Secondly, there is no reason why your socket circuit cannot be a ring circuit, from the workshop CU, while the main feed from house CU to your workshop CU is a radial (one wire) - in fact, that is the norm and the right way to do it.

It is the main supply from your house CU to the workshop CU which has the 20A MCB on it, and it is that circuit which is the limiting factor. If the 20A MCB is there because it needs to be there to protect the armoured cable to the shed, the proper way to do it is to see if it does serve your needs, and if not, replace the armoured cable with a bigger (single) cable.

Given the expense, let's hope the 20A circuit will be enough (as, in all probability, it will be).

Turn the fan heaters off while you are sawing!

Heaters?? I wish no artificial heating in my workshop at the moment, I brave the cold with just a fleece and a wee dram to keep me warm!

Digit - thanks, out of interest I'll take a look on google and get a little more educated

 

[Digit]

If you use electric heating choose a unit that does not use red hot heating elements as the smell of burning sawdust can be a great cure for constipation! :lol: