Discuss Continuity testing help in the Electrical Forum area at ElectriciansForums.net

tommybasin

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Hi, I created a thread on ultimatehandyman (yes I know) but I feel like I'd be better off posting my question here, you're welcome to have a look at the thread for full details however (Continuity testing. - http://www.ultimatehandyman.co.uk/forum1/post785195.html#p785195). I fully expect part of (if not all) what I'm assuming to be wrong, so please if you can explain what it is I'm not understanding.

A less long winded but still probably confusing way of asking what I want though is the following.:

Should appliances plugged into sockets be affecting end to end tests when checking the continuity of a broken ring - giving you a high ohms reading instead of no reading at all?

If not, why not? And if so, how do you work around this in a real life testing situation - if you do at all?

I hope that's clear, but if not the thread linked may shed more light (or just confuse you even more).

I'm not a DIYer trying my hand at a rewire, trying to gain inside knowledge or anything like that. I'm just trying to wrap my head around continuity testing and the limitations/issues you can have (if any) when belling wires out with a voltage meter with no LCD display.

Any help and explanation appreciated.
 

SparkyChick

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No they should not be affecting end to end continuity tests.

Why, because what you're testing is the conductors on the ring one at a time and the connections they are involved with (i.e. the terminals in the various accessories connected to the ring). What's connected to those accessories doesn't come into it. If you were testing between say line and neutral then they could come into play, but you're not, you're testing one conductor at a time and it's various terminations.
 

SparkyChick

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Welcome to the forums btw :)
 

TJ Anderson

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A cpc could be affected by it but not L-L and N -N. Particularly if you didn't take wires out at a origin of circuit and they were still connected at DB earthing terminal. For example, you could have a a cpc pulled out in a boiler spur on the ring. The boiler would be connected to pipework, itself possibly already at earth potential via bonding and it would complete the ring through that and not the cpc.
 

SparkyChick

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A cpc could be affected by it but not L-L and N -N. Particularly if you didn't take wires out at a origin of circuit and they were still connected at DB earthing terminal. For example, you could have a a cpc pulled out in a boiler spur on the ring. The boiler would be connected to pipework, itself possibly already at earth potential via bonding and it would complete the ring through that and not the cpc.
Very good point :)
 

Pete999

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Hi, I created a thread on ultimatehandyman (yes I know) but I feel like I'd be better off posting my question here, you're welcome to have a look at the thread for full details however (Continuity testing. - http://www.ultimatehandyman.co.uk/forum1/post785195.html#p785195). I fully expect part of (if not all) what I'm assuming to be wrong, so please if you can explain what it is I'm not understanding.

A less long winded but still probably confusing way of asking what I want though is the following.:

Should appliances plugged into sockets be affecting end to end tests when checking the continuity of a broken ring - giving you a high ohms reading instead of no reading at all?

If not, why not? And if so, how do you work around this in a real life testing situation - if you do at all?

I hope that's clear, but if not the thread linked may shed more light (or just confuse you even more).

I'm not a DIYer trying my hand at a rewire, trying to gain inside knowledge or anything like that. I'm just trying to wrap my head around continuity testing and the limitations/issues you can have (if any) when belling wires out with a voltage meter with no LCD display.

Any help and explanation appreciated.
With regard to "belling out" it's not an ideal way of testing for continuity, it used to be done that way but now with all the paperwork required for testing, the right test equipment is a vital requirement, there ar many videos available on youtube regarding continuity test, I suggest you sit yourself down and feast your eyes on some very knowledgeable engineers explaining the principles required, have a look and if you have some questions regarding continuity testing, we as Mentors can take a look as well and try to help you understnd.
 
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T

tommybasin

EF Member
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Location
gb
Cheers for the replies :)

SparkyChick, just a quick question to help me understand, as what you are saying is how I originally understood continuity testing to work until I found out that switching sockets (with appliances connected to them) on and off was affecting my bell tests (and later my ohms readings).

What is the reason (scientific I suppose) that the connected appliances will not affect the reading, considering the L&N will technically be 'connected' in the appliance? I explain what I mean in the thread linked with the awful drawing I made:D

I realise I'm wrong here, I'm just trying to wrap my head around why.
 

SparkyChick

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Cheers for the replies :)

SparkyChick, just a quick question to help me understand, as what you are saying is how I originally understood continuity testing to work until I found out that switching sockets (with appliances connected to them) on and off was affecting my bell tests (and later my ohms readings).

What is the reason (scientific I suppose) that the connected appliances will not affect the reading, considering the L&N will technically be 'connected' in the appliance? I explain what I mean in the thread linked with the awful drawing I made:D

I realise I'm wrong here, I'm just trying to wrap my head around why.
I see what you're getting at and you are correct, it could affect the results, however... when we test a ring for continuity, we're looking for resistance readings of typically less than 1 ohm. Anything more than that and we'd be worried that something was wrong and we'd be investigating.

If you consider most appliances, they are going to contribute way more than 1 ohm to the reading, especially given the configuration you're considering. If you had two kettles for example doing what you're suggesting, they might be contributing somewhere in the region of 40 ohms of resistance, that would be like UH OH!!! Fault!

A lot of modern electronics won't interfere in this way I believe, this kind of interference is likely to come from loads that are predominantly resistive, like electric heaters, kettles, toasters and those that use old fashioned transformers (as opposed to switch mode power supplies for example).
 
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tommybasin

EF Member
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Location
gb
That's great, thank you very much for bearing with me. I was going mad thinking I'd missed something major.

And coincidentally it was the kettle that I was switching off that was changing the reading :)
 

Grezza

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36
Location
Liverpool
Resistance always finds the easiest path which is usually the shortest route from one point to another, so if an appliance is plugged in a current would prefer to travel down the other leg of the ring rather than through an appliance and back out.

Testing ir on line to neutral at 250v will also help you see if an appliance is still in service on the circuit. A low reading such as 0.1 0.2 .
 

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