Parallel earth paths

[derykmarl]

Bit of a PAT testing newbie question, having been enlisted to in-service inspection and test all our electrical equipment (*cough* "PAT test") everything with a 3 pin plug on it (maintenance does the non 3 pin plug stuff).

Found an object that is a new case to me: in our engineering department is a big old drill on a big metal stand. 3 pin plug, so I have to PAT test it. The PAT420 machine we use then grumbles that there's a parallel earth path. Turns out the whole thing is bolted right into the ground! Ground... ah.... parallel earth path. Right. I don't think they taught us this in the course, or if they did, it was just "yeah unplug the monitor from the PC before testing it".

What am I supposed to do? I can't find much in the guidance or the tester's manual other than to just be "aware" of it. Surely I don't have to try and unbolt it from the floor?

I also can't get a reading that passes without lead compensation yet, and can't find a spec embossed on the flex so am not sure how I'd calculate that.

 

[Geoff1946]

I don't know the tester you have but I would be looking to satisfy myself that there was good earth continuity through the mains plug to the machine frame and that the insulation is good. Can your tester do that? Potential problem is that there is surely a contactor incorporated which prevents you switching on. Some testers allow a leakage test whilst operating.
The comment on "lead compensation" is of concern. Is it very long or thin? It shouldn't give more than about 0.25 ohm at most ? What's it showing? That could be justification for a fail especially in a workshop environment, and then your job is done.
Otherwise it sounds like a contender for maintenance department to check. Doing that task with limited electrical expertise you should err on the side of safety.
As with all PAT work by far the most important part is a thorough visual inspection.

 

[Phoenix]

I am not sure what the limit for parallel earth paths is on that tester even though its one I am familar with and have had the message a few times, but the result you'd be looking at for it to pass would have to be significantly better than anything you might get through it being bolted to the floor, so I'd be supprised if it detected enough of a reading to throw rattle out pram over that, are you are there is not another earth path, drill body pushed up against the steelwork, cross bond onto a cable tray etc

 

[poni]

Turns out the whole thing is bolted right into the ground

how portable is this thing?
Portable
Appliance
Testing
get them to fit a fused connection unit for this, that should fix both problems

I also can't get a reading that passes without lead compensation yet, and can't find a spec embossed on the flex so am not sure how I'd calculate that

how long is the lead?

 

[johnb2713]

Found an object that is a new case to me: in our engineering department is a big old drill on a big metal stand. 3 pin plug, so I have to PAT test it. The PAT420 machine we use then grumbles that there's a parallel earth path. Turns out the whole thing is bolted right into the ground! Ground... ah.... parallel earth path. Right. I don't think they taught us this in the course, or if they did, it was just "yeah unplug the monitor from the PC before testing it".

Surely thats NOT a 'Portable' appliance?

 

[binky]

Surely thats NOT a 'Portable' appliance?

Testing of non portable equipment seems to be popular, some examples I've encountered include built in kitchen appliances and gas boilers

 

[kerching]

Testing of non portable equipment seems to be popular, some examples I've encountered include built in kitchen appliances and gas boilers

Yeah but at 27p per item every little helps

 

[Fleeting]

The fact it is not 'portable' is not relevant and the term PATest is dated and misused. Under PUWER 1998 as well as other statutory documents this item of equipment needs to be maintained to verify its safety.
Ditch your tester and use a continuity tester.

 

[johnb2713]

The fact it is not 'portable' is not relevant and the term PATest is dated and misused. Under PUWER 1998 as well as other statutory documents this item of equipment needs to be maintained to verify its safety.
Ditch your tester and use a continuity tester.

As always, I'm indebted to your knowledge and understanding, PAT testing isnt maintaining a device is testing it.

also (as usual) I've done a little research:

From current HSE on the .gov site

 

[derykmarl]

Thanks for the feedback. I might just, as suggested, leave this one to the more experienced!

It does need to at least have a formal (recorded) visual inspection - they renamed it from "Portable Appliance Testing" to "In-service inspection and testing of electrical equipment" and removed ALL references to "portable equipment" from the code of practice for a reason, namely that it no longer only applies to portable equipment. Quite right because you can still get a shock from something that isn't portable! You can just usually decide to lengthen the interval (something else that is now left to the dutyholder to decide, or more likely to delegate to the competent person doing the inspection to "advise" them) based on the fact that, you know, no one is going to be dropping it or throwing it around.

As mentioned though the actual testing isn't a legal requirement. It's not just a box ticking exercise any more and the IET wanted to shift people away from "just blindly plug everything portable into a machine, press a button and slap a sticker on" and more towards "actually inspect electrical equipment for safety and understand what you're looking at" since most faults are identifiable visually so it's more like a risk assessment with guidelines (and testing remains a good way to prove something is safe), but I still want to understand what's going on before I bet anyone's health/life (and my freedom) on guaranteeing something is safe to use.

I can understand where they're coming from. Shifting the emphasis more towards inspection is trying to improve upon two problems 1) unsafe equipment being passed because "magic box said it was okay" even though you can see scorch marks on it or there's a crumpled up bit of foil in the plug in place of a fuse, and 2) the waste created by perfectly fine equipment being failed because "magic box says no" and the person operating the magic box not understanding why (for example because it has a 10m input lead).

If it's not due to being bolted to ground I can only assume it's because it's next to another metallic object maybe, not pushed up against it but a fair bit of scrap metal in between (literally used for drilling metal)

The tester does let you continue earth bond testing after the message comes up and returns like 0.11 ohms (limit is <=0.1+R where R is the resistance of the supply cable) so yeah hence I'm looking at the flex feeding it. It's not long, like 2m. 5th edition of the code of practice does allow for a little bit of wiggle room (up to 0.5 ohms) for older equipment as well as lead compensation. It does always say at least 0.06 or so though even on something brand new and perfect so if that's higher than is normally expected maybe I need to be looking more towards "you guys did actually follow the calibration schedule on the tester right?"

 

[joolsmy]

Bit of a PAT testing newbie question, having been enlisted to in-service inspection and test all our electrical equipment (*cough* "PAT test") everything with a 3 pin plug on it (maintenance does the non 3 pin plug stuff).

Found an object that is a new case to me: in our engineering department is a big old drill on a big metal stand. 3 pin plug, so I have to PAT test it. The PAT420 machine we use then grumbles that there's a parallel earth path. Turns out the whole thing is bolted right into the ground! Ground... ah.... parallel earth path. Right. I don't think they taught us this in the course, or if they did, it was just "yeah unplug the monitor from the PC before testing it".

What am I supposed to do? I can't find much in the guidance or the tester's manual other than to just be "aware" of it. Surely I don't have to try and unbolt it from the floor?

I also can't get a reading that passes without lead compensation yet, and can't find a spec embossed on the flex so am not sure how I'd calculate that.

WRT the flex you can compare its diameter with some known samples and base your compensation on the one that looks nearest in diameter.

Is the metal stand actually bonded or is the parallel earth literally through the floor? If the former you could try undoing the bond - although admittedly I've never resorted to this. If I can't eliminate the parallel warning I make a point of double-checking the plug and the flex and am only happy if there's a fair margin of safety in the reading.

Is it an old drill? The latest COP (5th edition) allows up to 0.5 ohm (after flex compensation) as long as you can satisfy yourself that the high reading is due only to the design of appliance and not a duff connection.
Edit: I see you've just covered a lot of this above.

 

[derykmarl]

WRT the flex you can compare its diameter with some known samples and base your compensation on the one that looks nearest in diameter.

Is the metal stand actually bonded or is the parallel earth literally through the floor? If the former you could try undoing the bond - although admittedly I've never resorted to this. If I can't eliminate the parallel warning I make a point of double-checking the plug and the flex and am only happy if there's a fair margin of safety in the reading.

Is it an old drill? The latest COP (5th edition) allows up to 0.5 ohm (after flex compensation) as long as you can satisfy yourself that the high reading is due only to the design of appliance and not a duff connection.
Edit: I see you've just covered a lot of this above.

From what I've seen similar flex is almost always 0.75mm^2 (can't think of the last time I saw any different in fact other than typically 1.0mm on extension leads) and this doesn't look any different. I'm not unduly worried as yes it's ancient and even if the cable CSA was 1.5 (which I very much doubt) it allows for 0.0266ohm of wiggle room at 2m and it's only over by 0.01. I just wanted to understand the parallel earth path situation and what it means so that I'm not passing something I shouldn't.

I'm no expert on drill machine terminology but google calls it a floor mounted drill press, seemingly. It's not literally bonded to earth but rather I think it's picking up the parallel path because that's where the giant bolts holding it down are going.