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Thread: Help with electrics.
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05-10-2019, 08:12 PM #21
Thanks Frim,no I would never check a live wire mate as I am soon cautiouwith elects.
It is a cheap dt 9250a with all sorts of knobs on.John
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05-10-2019, 08:19 PM #22
If the insulation on the cables is squashed together enough it is possible to get an RCD to trip without physical contact between the conductors of the cables. Induced voltages is fairly common, more so with 3 phase wiring or when cables of different voltages are run in close proximity and the insulation of the lower voltage cable isn't rated at the same voltage as the higher voltage cables. Like a cooker cable and a bell wire possibly?
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05-10-2019, 08:23 PM #23
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05-10-2019, 08:26 PM #24
Attachment 29702Attachment 29703Attachment 29704
Couple of pics of it Frim,all double Dutch to meJohn
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05-10-2019, 08:44 PM #25
That is currently set to 20 million ohms. To check the heater's resistance turn the dial back anti clockwise to where it shows a yellow 200 which is 200 ohms. Ohms is what resistance is measured in. To try to check the live and neutral cables resistance to the case turn the dial clockwise to the yellow 200 M. That is 200 million ohms. You may need to turn it to yellow 20 M to get a more accurate reading. If the leads on the tester are brown and blue put the blue into the hole marked COM and the brown into the right hand hole marked V. If you have red and black leads instead put the red where I said where the brown goes and the black where the blue goes.
Hope that makes sense?
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05-10-2019, 08:50 PM #26
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05-10-2019, 08:51 PM #27
I've just been able to see the photos on the first post and it looks like the consumer unit doesn't have any RCD protection? It's an old MK Sentry consumer unit with just a main switch and MCBs. Your powerbreaker plug is a 30 mA RCD though.
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05-10-2019, 08:58 PM #28
It is an old consumer as my mate fitted it for me who is or was an electrician,been fitted in the garage 17yrs and that was second hand from the house when a new one was fitted.
John
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05-10-2019, 10:57 PM #29
Frim might pretend he's daft sometimes and likes to joke about (usually offending someone each time, mainly Ann), but when it comes to stuff like this he's there to help in a flash and his electrical knowledge has helped so many.
You're a top man Frim.
Hope you get everything sorted John, just make sure your juice is off before prodding your wand into small holes, especially wet ones.
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06-10-2019, 01:06 AM #30
Thanks RS.
When it's something I know about I try to help if I can
I try not to offend Anne anymore these days.
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06-10-2019, 08:06 AM #31John
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06-10-2019, 08:18 AM #32
Rcd
Frim, so the unit is no good really
What's the difference between mcb and rcd ?
What does resistance mean?
Have my dial set on 200 ohms to check resistance.
To check if the live or neutral is shorting against the case i set it to yellow 200m ?
What do I touch the terminals to?
And what readings should I be looking for?John
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06-10-2019, 10:28 AM #33
Basically an MCB is the modern version of a fuse and will trip off if you try to overload it and run too much power throught it plus it will trip off if it detects a fault either between live and neutral or live to earth as it reads or detects that as an overload just like a fuse does. OK?
An RCD is designed to trip off if it detects a fault between live to earth or neutral to earth but unlike a fuse or MCB it doesn't trip off if you run too much power through it and overload it basically. It can detect the difference between a fault to earth and just a basic overload if that makes sense?
There is also an RCBO and that is a combination of an MCB and an RCD so trips out on faults to earth and overloads. So best of both worlds if you like. Does that make sense?
As for changing your consumer unit John, if I am correct and it only has a main switch and not an RCD main switch, any time you add anything to any circuit other than just plugging something in it should be RCD protected. For anything added that has a rating of up to 3 KW or 13 amps you can fit an RCD spur in the circuit to protect it quite easily but when you want to add to a circuit rated above 3 KW or 13 amps then it can get more tricky as you then need to add an RCD in an enclosure which can be more difficult to find space for, if that makes sense.
As the regs changed in January this year more things have to be RCD protected which is basically forcing more consumer units to be changed so if you can add RCD protection either directly to your consumer unit or externally via RCD spurs or RCDs in enclosures then you don't need to change your consumer unit just yet.
There are other things to consider now like surge protection devices SPDs and possibly ark fault protection devices AFPDs but that's another story altogether.
Resistance is the measurable value of a length of cable with regards to its ability to flow electricity through it basically.
For a 1000 watt or 1 KW element you should be getting a reading of 60 ohms. So put the lead from the terminal marked COM to one of the cables for the heater and the lead from the right hand terminal marked V to the other cable for the heater and to get a decent reading you may need to pinch the leads onto the cables either by hand or by using connector strips etc.
Once you have a reading in ohms if you get one at all as the element may be faulty set the tester to the yellow 20 M setting and test from each cable at a time to the metal casing of the element. As your tester is only working at a very low voltage it may not be capable of getting a true reading from the cables to the casing as this usually requires a tester called an insulation resistance tester which produces a voltage of 240 volts, 500 volts or 1000 volts so it gets a proper reading. But you may be lucky and your tester will give you a reading. You are looking for a reading of 0.5 M ohms or above from the cables to the case.
What you could try to see if your tester is reading bigger resistance readings is get a bowl of water and with the tester set to 20 M put the tips of the tester probes into the water and see what reading you get. You should find as you move the probes closer together the readings will drop and will rise as you move them further apart. You may find that you need to adjust the setting on the tester as the water is a good conductor of electricity so will have a low reading when set to a higher resistance setting. Another thing to try is hold the probes of the tester in each hand and it will read your resistance. Again you may need to adjust the settings to get a reading. As the tester is a multi meter it doesn't give off enough voltage for you to even feel it but if you are worried try it out on someone else first.
Hope that answers your questions John?
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06-10-2019, 12:19 PM #34
Ok Frim, set my meter on yellow 20m touched each terminal in turn to ground on heater and got minus - 1.26 on both !!
On touching both terminals meter on 20m reading zero.
On 200m reading 01.0
What is that saying Frim?John
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06-10-2019, 03:30 PM #35
'' HAPPY BIRTHDAY FRIM ''
Hope your having a good one
RS......with an E for gaud sake...……………………………….
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06-10-2019, 03:34 PM #36
Hey Anne missed that.
Happy birthday Frim,sorry for all the questions on your b/day,have a great one mate.John
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06-10-2019, 05:30 PM #37
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06-10-2019, 06:50 PM #38
Happy birthday mate Jurassic but a classic pal
Sent from my SM-N950F using TapatalkFreddyboy the legend
"we are water keepers first"
Johnathan
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06-10-2019, 07:15 PM #39
Nice one Ann e for spotting Frim's birthday.
Happy birthday Frim.
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06-10-2019, 07:19 PM #40
The 01.0 could be 1 million ohms possibly? As for the - 1.26 that could be 1.26 million ohms possibly? Anything over 0.5 million ohms is usually OK but as your tester is only using a very low voltage to read the resistance it may not be capable of getting the same reading an insulation resistant tester gets as that works by producing 250 to 1000 volts to carry out the test so if cables are breaking down the tester can pick that up as 250 volts will jump a bigger gap and give a more accurate reading. So it's quite possible that your element is faulty and shorting down to the case? What was the resistance of the element itself John?
Hope you understand all that
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