Portable Appliance Testing, woohoo...

[Ben Steele]

Hey guy's,

Hope your all well.

For thoso of you who haven't spoken to me befor, i'm a trainee! Wippee...
And most of the time in need of a little help.

I have a couple of question's which i dont know the answe's to and i'm a little stuck!

If there is someone who could help, i would be so greatful

(Portable Appliances Testing) "My Favourite"


Class 1, Calss 2, Class 3.

1, Earthed
2, Double Insulated
3, SELV


For a class 1 appliance does the continuity reading have be within 1 Ohm? if so, why is this?

Also, im not to sure on what the insulation resistance results be within, for a class 1,2 and 3 either.

Could anyone shed some light for me please?

Many Thanks

Ben Steele.

 

[crabapple]

EARTH CONTINUITY

Class I <0.1 ohm
Class II <o.1 ohm
Extension Leads <0.1ohm

should be as low as poss so as not to impede any fault currents

INSULATION RESISTANCE

class 1 >1Mohm
class II >2Mohm
extension lead >1Mohm

these are min acceptable values for the quality of the insulation, any less and its rubbish

 

[Ben Steele]

You the man!

Thanks for the help buddy.

 

[xraytek]

EARTH CONTINUITY
Extension Leads <0.1ohm

should be as low as poss so as not to impede any fault currents

As far as I am aware the <0.1ohm figure doesnt apply to extension leads.
The maximum permitted length for a 1.5mm squared extension lead is 15 metres which equates to 0.2ohms.
The IEE guide says that an RCD plug is required if a lead is any longer, and that any load must be considered so that voltage drop is avoided.

 

[roukel01]

Class II Earth continuity <0.1 ohm ??

Since when does class II equipment have an earth to measure continuity?

 

[peteludman]

that is true mate

 

[Ben Steele]

Hey All,

Thanks for the replys,

Double insulated being earthed! easy to catch yourself out hey! there's nothing worse than trying to look for something which was never there in the first place ha ha...


Earth Continuity.

Now i know what the reading should be i guess it would now be time to ask why it has to be within 1ohm?

My thoughts are...

To measure the time it takes for the fault leakadge to get to the trip and cut off the supply!

Also for the insulation resistance,

You run a current through the live and neutral and then measure the resistance via the earth. is this right?

This is going to sound like a very stupid question! get ready...

When you are measuring the resistance, what are you actually looking for?
As in, if the reading comes back to high, what would be the out come?


Thanks for putting up with my ignorance guy's, Really appreciated.

Many Thanks,

Ben.

 

[roukel01]

When you're PAT testing you attach a wander earth lead to a metal part of the equipment, and test the resistance between the case and the earth in the plug.
The lower resistance the better because if you have too high a reading then in fault conditions the metal could become live without blowing the fuse/mcb because the earth path is insufficient to carry the fault.

 

[xraytek]

When you are measuring the resistance, what are you actually looking for?
As in, if the reading comes back to high, what would be the out come?

You are looking for a nice low continuity result, and nice high insulation test result.
The <0.1 ohm measurement is between any exposed conductive part, and the main earth point of the appliance ( not the earth pin of the plug). This means that you can deduct the cable resistance from the test result Although in practice the reading is usually well within 0.1 even with the lead included.

 

[Ben Steele]

Hey Guys,

Thanks for the replys


It's all begining to make sense now, wipee.

I suppose there's only so much one can learn about PAT testing hey!

Really appreciate the help guys

On a different note, i started collage monday, woohoo. I'm at JTL at the airport industrial estate doing a 4 year advanced apprenticeship.
Dont know if anyone from the forum has or is going there, but it seem's like a very friendly enviroment.

My instructor is Jon Barrett, and what a funny guy he is, he has a very open sense of humer and can turn anything into something smutty! I asked if he had some spare tissue (for my nose) well that was it,you can only imagian the response i had coming!

In a way, i suppose it's a breath of fresh air to have a tutor who actually enjoys teaching and has a sense of humer to go with it. Makes it easer on the leanring i guess.

Thanks againe for the help all, reall really appreciated.

Many Thanks,
Ben.

 

[Ben Steele]

Hi all, Me again

Just a quick one for ya!

When doing a insulation resistance test on a class 1 appliance, you measure the leakage via the earth right?

So how do you measure the resistance on a class 2 appliance? there's no earth!

Got to do an presentation on PAT testing in front of the class and it suddenly occured to me when i started going through note's, that i haven't got a f*****g clue!

Sorry to keep asking stupid questions.


Thanks all,

Ben.

 

[xraytek]

When doing a insulation resistance test on a class 1 appliance, you measure the leakage via the earth right?

Sort of I guess... With an IR test the meter puts a voltage across L & E then measures the current flow, and from this calculates the resistance (Ohms law).

So how do you measure the resistance on a class 2 appliance? there's no earth!

You dont measure continuity because as you say there is no earth. But you can look for any accessable metal parts on the appliance (like screw heads etc) and connect the earth probe to it for an IR test. The test is to ensure that metalic parts are insulated from the live conductors.