Thread: Electrical help connecting a motor - where should these go?

Hi,

Following on from an older thread about using the bench drill motor for the lathe, I've got a question for the electrically minded people out there.

This may be a very simple one but I've not played with 240 volts before, and rather be safe than sorry!

As per the attached diagram I need to know where the earth (green / yellow) leads would be best. The motor will be mounted on an alloy plate in no way connected to the metal lathe chassis that the switches will be mounted on.

Am I best to have one of the earth leads attached to the metal plate, and the other to the chassis of the lathe alone, and should these also be joined by another lead connecting the alloy plate and the lathe chassis?

In the drill press the 'stuff' came out of, they are both connected to the metal chassis about 1 inch apart (standard fitment I would imagine on just about all drills), but obviously as per my pic the 2 (motor and switches) are separate now. Does the alloy plate even need to have the earth lead connected to it?

Any help much appreciated.

THanks.

COlin

It might make things clearer if you can identify where each earth wire comes from. That will make it easier to decide where they must go to.
The bottom line is you should earth all metal parts, to the same point, so that you have protection ( the fuse blows) if a fault develops, so, if the two earth wires come from different components, it would be simple to just connect them both to one part of the machine and then run another earth from that connection to the other unearthed part. Hope this helps.

Holy cow, I cant believe these questions, this is 240 v you're playing with, it can kill ya stone dead.
Next thing we see will be queries about diy brain surgery. Jon.

Hi, thanks for the input.

Just to clarify, I'm not trying to re-invent the wheel here, simply a 'transplant' of the switch and motor from an already functioning drill press onto a lathe.

The green / yellow wire: One comes in from the wall plug, the other is from the actual motor. Obviously these two must be 'connected' as you say. On the original drill press they obviously received continuity by being on the metal body of the drill.

As the switch does not appear to need to be gounded (by virtue that it is all plastic), could I simply run both of these to the alloy plate the motor is mounted on?

Thanks again for any further input.

Colin

Hi Colin,
The last thing we want is to hear on this forum is, of someone getting being electrocuted or burnt in a house electrical fire. Possibly, home electrics is a DIY activity that quote " everyone does".seems to be the line of thought ?
I know my humble opinion will differ from others on the board, but if you do your own electrical work and are not a licensed person, this forum is not the place to mention it.

The electrical regualtions don't allow for home DIYers messing with electrical equipment that is within the province of licensed electrical trades people. That is why they have to be licensed .Electricians are held responsible by law for the work that they do.

If you do your own wiring, and get it wrong you might burn down your house or maybe even injure or kill a person.
Please ,if you are not dead sure about that, you could be dead for sure.

I am sure you will hear more on this thread from the sparkies themselves.We would like to see you around the forum for many more posts to come.

Please don't put yourself or others at risk.

Grahame

"As the switch does not appear to need to be gounded (by virtue that it is all plastic), could I simply run both of these to the alloy plate the motor is mounted on?"

Yeah, that seems ok. It's more important that the two Earths are joined together as that will mean the motor is properly Earthed. Check the Earth continuity of the motor before you use it to make sure. It should be less than 2 ohms, I think.

It's 240V and deadly, so if you don't know how to do it, then don't do it.
It's just not worth the risk.

macca

Originally Posted by Grahame Collins

I know my humble opinion will differ from others on the board, but if you do your own electrical work and are not a licensed person, this forum is not the place to mention it.

I fully agree with your opinion. I won't give out electrical advice in these forums either.

Take it to an electrician and get it done safely.


Peter.

In WA any electrical appliance with a power cord on it that goes into 240 volts can be serviced or modified by anybody. If the wiring is hard wired to a house then it needs a qualified electricain to install it. As you can see common sense prevails, if it required an electrician for every electrical appliance then nobody would be able to sell a single electrical item as they would require an electrcian to do the final wiring. Now your question, you will see some items only require 2 prongs on the 240v plug ans ssome items require three. The difference is the earth circuit, which is straight out a safety circuit. On any item which is all steel ect on the xeterior of the product and there is a risk of a power wire contacting that surface it requires that part to be earthed, and thereby tripping a circuit breaker to cut power. Items which are insulated in platsic. that is they are housed in a plastic item example portable stereos and small transformer packs only will use two wires as there is no risk to the consumer of a loose power wire touching the housing and transferring the current. In your scenario " I would simply " connect the earth lead to the body of the unit, its that simple
Steve

Thanks for the input, all opinions are valued.

While I certainly don't advocate DIY full scale electrics either - usual disclaimer here - (I know 240v can kill, I've been 'bitten' several times over the years - electric fences etc - with much less so this is definately something I want to avoid), however I would have thought the process of simply 'transplanting' the switch and motor (with complete undamaged wiring loom), from one machine to another was pretty straightforward. I'm not modifying the plug, switches or motor in anyway, purely an install. I cannot see how this is much different (possibly less dangerous) than those who ask advice on converting machines from single phase to 3 phase and vice versa, and wiring up different motors, variable speed controllers etc etc, I'm sure all these people aren't electricians.

Thanks Simso and Sterob for the detailed explanations. I agree with WA's laws on this one, by other logic I should have taken our microwave to a licenced electrician to replace an .80c fuse when it stopped, at a cost of who knows how much (yes I know you can't put a cost on human life but let's be realistic - I'm not exactly rewiring a house here - the worst that would have happened was the circuit breaker blew, which was exactly what happened in the first place - incidentally..the microwave has been working fine now for many months and I've enjoyed many a hot meal!).

Thanks again for all input.

Colin

I agree with all the don't do it posts.
I've wired everything within cooee of my house/shed/pump house....got the strap from the electrical inspector for being too neat.
But, if I get zapped....or my Missus gets zapped, or any visitor gets zapped.....the buck stops with me.
The answer is...DON'T DO IT!! (sorry for shouting)
On another thread we were talking about recycled washing machine motors/starting capacitors and wiring..again we should also all say get an electrician. DIY electricity isn't a place we should go

I agree with the above answers if you are unsure ask a sparky

Colin
Even though some forumites may ridicule me for this post I offer the following-
From your thread as I understand it there are three metal components being the motor body, the alloy mounting plate for the motor and the lathe mounting frame that the switch is mounted on.
Firstly you should not rely on a bolted connection between two metal parts for continuity for earthing purposes and so both the motor and alloy mounting plate should each have an earth connection. Now you have mounted the switch onto the lathe mounting frame and despite the fact that the body of the switch is plastic, the frame should also be earthed because of the possibility that metal parts could come in contact with a live conductor (eg vibration causing loss of cable insulation).
An earth connection to the metal parts other than the motor is best made by crimping a suitable lug onto the earth lead and bolting it to a dedicated bolt fixed to each of the plate and lathe mounting frame.
The three earth leads should be brought together at the supply point being the switch box.
I am not able to give advice about earth lead size and have only provided the above information for your understanding. I suggest that it really is a job for an electrician, at least to ensure compliance and safety.

Regards from Adelaide
Trevor

Hi trevor,

Thanks for the info.

This is essentially what I thought (have also been doing some reading on electrical sites). I was thinking of using standard Earthing cable (from an old power cable - ensuring in good condition and same size as the ones in the setup in question), and some good quality eye terminals to make any additional connections as required. Based on your info I would also run a connection point to the alloy plate as well as to one of the bolts holding the motor to it (removing the paint on metal surfaces to ensure a good connection), one of the existing earth leads already goes directly to the motor internally. It may be that I end up with 4 earth connections at different points (motor, alloy plate and lathe chassis x2), but again from my understanding, this presents no danger, if anything more safety.

I am going to do a diagram of this and get an electrician to check it over for me, but I don't see any problems with this.

Thanks again for all the input, has been much appreciated, and I will post my results.

Thanks.

COlin

Electrckery is one of those things (most of the time) where if you have to ask, then you shouldn't be doing it.

However, this is a plug in thing, and not hard wiring permanently connected to supply. Last time I checked, any nimrod can do whatever the heck they want with it.

And I'd trust someone that's not a sparky with half a clue than a licensed sparky that doesn't know what the heck they are doing.

If you are not sure, show a competant sparky.



(Anywhere a wire goes by/into a metal something, earth it with it's own screw that is only used to earth the thing, no other reason. Use the same wire through out, that means the same wire the flexible cord is made from. I didn't tell you that BTW.)



For all the doomsayers, I have a quandry for you.

I wired in a circuit in the workshop a while ago. From the breaker box to the outlet. I am not licensed to do this work, but I did it anyway because I needed the circuit and wasn't willing to find a local sparky to do it.

Was I wrong?