Fluke

[unclebubble]

I have just started doing testing and trying to find my way with a Fluke(can't remember model number)It's a combined loop/meggar/rcd.
When I am doing insulation resistance I believe I'm supposed to test at twice nominal voltage(ie 240 volts set it to 500)
If it is clear and nothing is damaged it comes up at 500 megohms(I actually thought it was supposed to be 1 megohm with a minmum of 0.5 so how does the 500 reading relate to this?.Also it sometimes take ages for it to reach this reading(2-3 mins doesn't matter if its l-e or l-n)sometimes it takes so long I just set it to 200 just to get the test done quicker!Does anyone else have this problem?Any help is appreciated!

 

[electronicsuk]

Anything above the minimum required resistance is OK, so 500MOhm (infinity to all intents and purposes) is fine, and what you would expect from short cable runs.

As for the time taken to reach this reading, is there anything else connected to the circuit you're measuring? How long are the cables you're testing? It sounds as it there might be a significant amount of capacitance somewhere in the circuit.

 

[unclebubble]

thanks for getting back!The tests are just done on a ring main on an average 3 bed house(grnd ring.1st floor ring and kitchen)I've made sure nothing is plugged in and all switched spurs are off!It sometimes takes a rediculous time and sometimes it will just hover at 400 and just keep beeping!

 

[Spark123]

a Fluke(can't remember model number)It's a combined loop/meggar/rcd.

Megger (brand name) = Insulation Resistance Tester if you don't want to fail your exams

When I am doing insulation resistance I believe I'm supposed to test at twice nominal voltage(ie 240 volts set it to 500)

Read your on site guide/GN3, it is all in there the test voltages and minimum IR values which are acceptable.

If it is clear and nothing is damaged it comes up at 500 megohms(I actually thought it was supposed to be 1 megohm with a minmum of 0.5 so how does the 500 reading relate to this?

The minimum IR reading for a 240v circuit is 0.5Meg Ohms, however any reading below 2Meg Ohms should be investigated further. As 500Meg Ohms is higher than 2Meg Ohms then this is fine. I am thinking you would benefit from some formal training i.e. college course?

Also it sometimes take ages for it to reach this reading(2-3 mins doesn't matter if its l-e or l-n)sometimes it takes so long I just set it to 200 just to get the test done quicker!Does anyone else have this problem?Any help is appreciated!

What do you mean by 200? The tests as outlined in GN3 require the IR test to be conducted at 500volts. This is the voltage that the test must be conducted.

 

[comms]

When I am doing insulation resistance I believe I'm supposed to test at twice nominal voltage(ie 240 volts set it to 500)
If it is clear and nothing is damaged it comes up at 500 megohms(I actually thought it was supposed to be 1 megohm with a minmum of 0.5 so how does the 500 reading relate to this?.

You wont always get >500Mohm, but so long as the reading is above 0.5Mohm it's a pass but if the reading is below 2Mohm then further investigation is required.

Also it sometimes take ages for it to reach this reading(2-3 mins doesn't matter if its l-e or l-n)

No problem with that, wait for the bleep or just mark down on cert >200Mohm if reading goes above that level.

sometimes it takes so long I just set it to 200 just to get the test done quicker!

I think youll find it's 250v on the meter setting & is used for elv circuits, so if youre using this setting youre not actually testing the circuit correctly are you.
The only time I use this setting on a non elv circuit is when I cant be sure I've found all plugged in equipment, it saves blowing some kit thats hidden away, find the offending item unplug then retest at 500v

sometimes it will just hover at 400 and just keep beeping

>400Mohm is fine & the beeping is telling you the test has been completed.

How are you getting on with the rest of the testing ?
Are you a trainee ?
I would advise some formal training if you've never undertaken any testing before.