Hi - Im getting my PCNC up and running now - very impressed.
Tormach advise using a RCD on the supply - for safety I suppose - so I fitted one. It is A 10Amp 2400 w 250V. But the current draw on motor start up is popping it out. i could probably get a bigger one but.....

I wonder if this is just Tormach being cautious - and how many users are really using them?

Like to hear your thoughts.

What is an RCD?

Mike

Residual Current Device - detects current leak to earth, shuts down power supply and can prevent electric shocks etc.

I take it you have a combo breaker, meaning it will trip on overload or earth leakage, you can get them with a higher overcurrent trip (20amps) and still have a 30milliamp leakage trip, this should solve your motor tripping problems.

We have to have RCD's on all power/light circuits here so I guess we are already covered :)

Cheers.

Russell.

In the US that is a GFI.

Its a type of combo breaker - but only surge and RCD - maybe the surge is tripping? anyway I have left it off for now - I suspect most of you run without one? Cheers

Dear keen,

RCD, ELCB, GFI or whatever... use one

The last thing you need when operating a machine or power tool (whether it is indoors or out) is a shock that puts your muscles into spasm. If you are lucky, you just get a spasm. The other end of the luck spectrum is instant death, and death, also, to the person who comes to rescue you.

The devices are mighty cheap compared to your life.

Sorry, please excuse the lecture...

Best wishes,

Martin

Good general advice Martin - thanks. I have checked the machine to actual earth and it is good - I would have to grab a live wire to be the preferred earth

But..........actually I had a bad hair day once and did virtually that.........hmmm..........

Good general advice Martin - thanks. I have checked the machine to actual earth and it is good - I would have to grab a live wire to be the preferred earth

But..........actually I had a bad hair day once and did virtually that.........hmmm..........

Dear keen,

One might cost you about £ UK 30 tops (sorry I do not have the NZ currency rate to hand).

30 mA trip
30 milliseconds

Get one now.. or value your life (and those close to you) quite cheaply.

(end of lecture)

Best wishes

Martin

I have several machines with coolant in operation - presumably the risk is about equal on all - do you mean a RCD on each machine or just one on the main board? In NZ RCD on each machine or on main board is very rare.
Cheers

I have several machines with coolant in operation - presumably the risk is about equal on all - do you mean a RCD on each machine or just one on the main board? In NZ RCD on each machine or on main board is very rare.
Cheers

Dear keen,

I'm really no expert on this, but I have a single RCD on the incoming supply, both at work and at home. My belief is that this gives reasonable protection to all devices "downstream" on each site. I could well be wrong.

It could be that if you have a remote shed some way from your house, you may need another means of protection. Eg. another earth electrode rod banged into the ground next to the shed, and maybe another RCD.

I speak from ignorance here, and there will be plenty of people on the Zone who will be of help.

Bring it on Guys..

Best wishes,

Martin

Of course, if you want to risk it...

http://www.youtube.com/watch?v=g0wmLzS3dt4

BW

Martin

I thought that Tormach recommended an RCD or GFCI on the 120 VAC circuit. I've installed one on mine, but did not do so on the 220 VAC line for main power, because I figure the VFD for the spindle motor wouldn't like it as the VFD on my lathe tripped instantly it was powered up from a GFCI-protected 220 VAC circuit.

Mike

I have checked the machine to actual earth and it is good - I would have to grab a live wire to be the preferred earth


This is assuming everything is working correctly, lets say that for whatever reason the earth connection breaks in the lead and there is a fault in the controller loose connection/bad insulation whatever... now everything metal on the machine is at mains potential, this may sound unlikely but there are a lot of deaths every year from this type of situation, I guess it comes down to either taking a bit of a gamble or making the odds a little better in your favour.

RCD's are not a guarantee of safety but they work well for most situations. When they became compulsory here there was a bit of a carry on as fridges had a habit of tripping them and they were the old earth leakage type that used to trip if you looked at them the wrong way, but RCD's are better these days.

I would recommend an RCD per circuit, even for industrial situations, which seem to be neglected for some reason, most people would shrug their shoulders at this and quote the cost, but as an electrician who has seen a few bad installations due to various reasons, that is purely my opinion.

Russell.

Thanks Russel and Mike - Mike that sounds like the problem - that its the VFD tripping it out. So I checked my manual and I can't find the advise on using a RCD - I now think I may have imagined I read it!

Keen - see page 2-7 in rev C2-3 of the manual, which is available at Tormach's web site. They recommend a GFI-protected circuit for the 120 VAC accessory outlet.

Mike

Thanks Mike - I wasnt dreaming!

Dear keen,

I'm really no expert on this, but I have a single RCD on the incoming supply, both at work and at home. My belief is that this gives reasonable protection to all devices "downstream" on each site. I could well be wrong.....

Just to be awkward, or maybe to stisfy his request to: "bring it on guys" I think a single RCD/GFI/whatever you call it is not a good approach. Use a separate one on each circuit to avoid nuisance shut downs of the entire system due to a fault in an individual circuit.

Hi Guys

Can you add an RCD to the 240 vac circuit or is the only way of installig one in combination with a Breaker? I have seen lots of GFI's for 120 vac circuits but have not actually seen a 240 volt unit. Who sells these?

Willy

I have about 6 altogether. I have a plug to plug type on my regular extension lead which stays there so I never forget to use it. On the two extension leads to my shed ( As martin knows ;) ) I have the plug wired in type ( Not what its really called :rolleyes: ) so I can't but use them! And a few spares lying around the place, I think there's one in my toolbox....

As an aside I recently made a little boo-boo wiring up an extension lead....I wired the neutral wire to the earth terminal without realising. Every time I plugged it in the RCD tripped....lucky me... :o


One might cost you about £ UK 30 tops (sorry I do not have the NZ currency rate to hand).

Less than €10 in B&Q.

I dont know about installing one into the mains circuit, your mains trip switch performs a similar function. I've only ever seen the plug type ones. If your using a multi socket extension lead, the lead itself should always be plugged into the RCD, which should always be plugged directly into the mains wall socket, essentially as far back along the circuit as you can get it. The individual items should not have an RCD each plugged into the extension sockets. Dont ask me why, it was in the instructions! :D

.... I have seen lots of GFI's for 120 vac circuits but have not actually seen a 240 volt unit. Who sells these? Willy

It is possible you will not find 240 volt units in Canada. Portable hand tools here are probably always on 120, in Europe/UK/Eire/Aust/NZ the standard is 240 so that is what hand tools are on unless a step down transformer is used.

One big difference between 120 and 240 is that 120 is not likely to kill you; 240 is likely to kill you.

Hi All - In NZ we have 240v and the units here are about $US 20 - in NZ they are usually only used for outside applications or where water is present.......
But seldom used in workshops etc - not safe practice now that i am thinking about it...........

Dear Geof, keen, and thkoutsidthebox,

I can see that there are circumstances where it is undesirable for the whole workshop to shut down in the event of some fault detected by an RCD. For example, if you run the shop vac. into a puddle of water and consequently shut down a $250,000 cnc machine doing something quite interesting, you may not be a happy bunny. You will however be alive to curse the fact that you failed to implement a circuit layout that prevented "nuisance tripping".

If nuisance tripping is likely to cause grief, it is, as Geof suggested, worth being selective where you put them. In my case, a global blackout doesn't matter, but it will to others.

In the UK, it is pretty much common practice now to have a 30 ms/ 30mA trip RCD on the main fuseboard for both isolation of the in-coming supply, and for protection of all cabling and outlets downstream . RCDs just measure the current in (1) the Live and (2) the Neutral conductors of the circuit. If there is a difference in those two currents, the RCD trips to specification.

Why??? because it means that the current in one conductor is going somewhere where it shouldn't, to Earth, and perhaps via your body, or perhaps via an arcing failed cable , appliance or whatever that may cause a fire.

If you have such an RCD on your main fuseboard, (£uk30) and then use another similar "plug top" B&Q (£uk10) one on a socket served by the main fuseboard, there is no guarantee that the plugtop one will trip before the one on the fuseboard when you have a problem in the shed. It could be that the plugtop trips first. If this happens, the house stays lit and the shed goes down. On the other hand, it could be that the main RCD wins this equal race, and you get the global black-out. You will however had the benefit of two RCDs trying, in the worst case, to save your life. (Spend that tenner at B&Q!!)



Best wishes,

Martin

I am assuming that RCD's are used now extensively in UK and AUS & NZ, probabally because of the method used for the ground circuit, I know when I was involved with this issue many years ago in the UK, the RCD was introduced because of the introduction of composite water supply pipes and these could no longer guarantee an adequate ground path back to the supply transformer ground, If this method of grounding is still used, it is different from N America practice, where the supply company provides a ground and it is connected to neutral at the service entrance.
In the UK it was then the case that the neutral was only grounded at one point, the star point of the supply transformer, and it was forbidden to connect the neutral at any other point, especially at the building service entry point.
In N. America, the common use of individual RCD or GFI is in washrooms and sockets external to a building.
Al.

..... RCDs just measure the current in (1) the Live and (2) the Neutral conductors of the circuit. If there is a difference in those two currents, the RCD trips to specification......

So that is how they work; and it also explains the name. I don't fully understand the GFCI and have no idea if it functions the same. I always thought it was looking for current in the ground line. If you only have two conductors, live and neutral as is common over here with hand tools, you cannot monitor a ground line but the RCD would still function.

live and neutral as is common over here with hand tools, you cannot monitor a ground line but the RCD would still function.

Geof, This is called 'Double Insulation' protection, but the GFI is still used because the tool itself can be at ground, i.e. the drill,saw, work piece etc, if for any reason the cable gets cut and comes in contact with a grounded (earth ground) ( or you drop it in water) piece of equipment and operator etc, then the unbalance will trip the GFI.
Al.

Thanks Al. I do often but not always use GFI equipped cords our outlets; I guess really I should always.

(Apologies to the thread instigator for the diversion below but it has some relevance.)

But here is a question for you; description of events first:

A person at our office a few weeks ago went to turn on their office lights and finished up semi-conscious on the floor about six feet from the light switch. They had two burns on the palm of their hand and beside the switch was a scorch mark on the wall. Our first aid person dealt with the shocked individual and I looked at the switch. When I operated it (with an insulated screwdriver) the switched arced internally and out through the slot that the toggle rides in. With the power turned off and the shockee now coherent and standing we determined that the distance between the burn marks matched the distance between the slot and the mark on the wall. Our conclusion was that as they swept their palm down over the switch to turn it on they got arced and the return path fortunately was primarily back into the wall with some passing through their body core to the floor.

My question is would a RCD/GFI have prevented something like this? Not that you are likely to find them on interior light circuits.

The event was somewhat unsettling; the circuit was a 347volt lighting circuit and the person involved my daughter. I checked and none of the 347v switches in the building had grounded fronts; needless to say by midday they had all been replaced with new grounded front switches.

It is common for lighting circuits in large installations to be fed from this high a voltage, the question I would have, iswhat is the insulation & voltage rating of the switch?
An arc over accident of this nature would probabally still occur with a GFI type device but it should trip right away, but the damage could already occur.
Personally I prefer to see these type of circuits switched using lower voltage switching, via contactor or relay.
I think you took a wise approach to ensure metal clad grounded switch enclosure.
Al.

It is common for lighting circuits in large installations to be fed from this high a voltage, the question I would have, iswhat is the insulation & voltage rating of the switch?.....Al.

The switch was the correct rating, etc. At least that is what it said on the side.

The thing I found amazing was that it is still possible to get 347v switches which do not have the grounded front.

Dear Goef,

IMVVHO, an RCD (if you can get one rated for 375 volts) would not have prevented the arcing or your daughter's shock, but it would trip out the circuit within say 30ms and before the overall fault current to earth exceeded 30 mA. If it behaved correctly, your daughter would barely have felt a thing, I think.

Best wishes,

Martin

Err.. that should have been "Geof" and "347 volts"

Oh dear..

Martin

To re-iterate, I think it is a bad practice, whether allowed or not, of bringing almost 400v down to what essentially is a light switch, I have seen a few hands that have been badly burned due to flash over when working on 480v panels etc.
The general method used in large shop floor layouts using contactor controlled lighting banks is much prefered, IMO. And probabally much cheaper than a 400v GFI.
Al.

To re-iterate, I think it is a bad practice, whether allowed or not, of bringing almost 400v down to what essentially is a light switch,..... Al.

Not essentially... it is a light switch.

And I agree with your sentiments, however, I am not sure I want to undergo the disruption and expense of ripping everything out and rewiring 3500 square feet of office space from a mix of 347 and 120 all onto 120 in a leased building. New switches should solve the problem for the next 20 or 30 years and we will be long gone from here by then. Or I will have bought the building and gutted it and redone everything.

Dear Al,

I absolutely agree. I find it quite incredible that you are allowed to have that voltage on a lightswitch especially if the switch controls lamps with a high inrush current on switch-on. Still, different countries, different Codes.

Best wishes,

Martin