Dishwasher Live!!

SpaceTime

I just want to confirm my theories here before I contact our new landlord.

Renting a very nice place, everything's high spec but last night I was unloading the dishwasher and noticed a slight tingle when I touched it.

I assumed it was static, but then got another 'buzz'.

At that stage, I got out the phase tester and touched it on the dishwasher door (nothing lit up) then I touched the interior of the cabinet and it lit up brightly!

Any of the stainless steel parts were live!

I was amazed the RCD or even, failing that the full MCB hadn't tripped so I decided to test a few other surfaces around the kitchen and nothing else was live (sink, cooker, etc)

I also checked the earth pins of a few plugs and nothing lit up (just in case there was an earth fault).

I then decided to very carefully plug the dishwasher back in and tested the earth pin and it lit the phase tester.

So, now I'm assuming we have two faults:

1) The socket's not earthed.
2) The dishwasher has an earth leakage fault.

Would you agree?

I am calling the landlord a.s.a.p. and obviously have completely unplugged the dishwasher in the meantime.

I am very concerned too that it did not trip the RCD.

It's connected to a surface-mounted socket under the sink, so I would assume it was installed by the kitchen installer rather than an electrician as the rest of the house seems to be earthed correctly and it's relatively new build.

I'm just wondering if they've done something daft like take a spur from the cooker circuit (i.e. no RCD) and also somehow managed not to connect the earth.

If there was a proper path back to earth, even without the RCD I would expect if it were a big enough leakage it would trip the 20A MCB or even blow the plug fuse (slower acting than the MCB usually).

tomdempsey200

you should train to be an electrician!!




1) The socket's not earthed.
2) The dishwasher has an earth leakage fault.

sounds about right....

SpaceTime

There were a few other little oddities like the washing machine was producing hot clothes on the final rinse. Checked the plumbing and discovered the whoever installed the valves managed to but the blue valve on the hot pipe and the red valve on the cold pipe.

So, the machine was rinsing with all our hot water!

Swapped the fill hose to the other valve, and it's now filling with cold water

Kitchen looks nice, but I have a funny feeling the installers weren't the greatest.

The phone line also failed a DSL prequal which seemed odd, well it would only support about 1mbit/s max according to their database.

I did a bit of investigating, and plugged in the phone, listened to the dial tone and it was all crackles and hisses. You could barely hear the line over the noise.

So, I went to the eircom NTU and isolated the internal wiring and plugged into the test socket and the line was absolutely perfect.

It turned out someone had pushed furniture too tightly against the wall and a large double-adaptor plugged into the master socket had basically smashed the faceplate module that sits into it so there was a loose connection which was hissing and crackling away for years!

There's no DSL account, but the DSLAM in the exchange is active and my own modem sync'd up with it and the line stats are about as close to perfect as you could get.
The previous occupant was apparently cursing eircom for years and it looks like the whole thing was down to the rather ropy internal wiring.

If I find any more weird things like this, I may have to move

....

I think the main thing now is to get an electrician and a dishwasher repair agent out to figure out what's going on!

---

Maybe I should just start a new business trouble-shooting homes or become an insurance assessor / building inspector lol

2011

SpaceTime wrote: »

I got out the phase tester and touched it on the dishwasher door (nothing lit up) then I touched the interior of the cabinet and it lit up brightly!

If you used a typical "phase tester / screwdriver" effort don't trust it.
These units are banned from many sites as they are very unreliable.
Therefore your test should not be relied upon.

Many accidents have occurred due to these "phase testers".
Professional electricians tend to use a proper test instrument (such as those made by Fluke or Robin) with very good reason

I was amazed the RCD or even, failing that the full MCB hadn't tripped so

Remember RCDs are not designed to trip if once ther is a current differential of any magnitude!

The type of RCDs normally used in a domestic installation is only designed operate if the current differential > or = 30mA. In this case the current differential may have been far less, but could still have been enough to give you a fair shock.

MCBs are over current devices. I am guessing that yours was a 20A B type (as this would be quite typical). It is very likely that the current flowing through the MCB was far, far less which would explain why the unit did not operate.

cerastes

2011 wrote: »

Remember RCDs are not designed to trip if once ther is a current differential of any magnitude!

The type of RCDs normally used in a domestic installation is only designed operate if the current differential > or = 30mA. In this case the current differential may have been far less, but could still have been enough to give you a fair shock.

MCBs are over current devices. I am guessing that yours was a 20A B type (as this would be quite typical). It is very likely that the current flowing through the MCB was far, far less which would explain why the unit did not operate.

I thought 30mA was meant to be quite low? given a fatal current can be at 80mA-120mA depending on the person and the insulation between them and ground?
Assuming the dishwasher isn't tripping out an RCD, does this not mean that the circuit it is on, is probably not supplied from an RCD.
But its something the OP could check by checking the consumer unit and see what is in use and then if necessary switching circuits off and determining if it is a faulty RCD but not by touching the dishwasher to test.

SpaceTime

If you used a typical "phase tester / screwdriver" effort don't trust it.
These units are banned from many sites as they are very unreliable.
Therefore your test should not be relied upon.

Many accidents have occurred due to these "phase testers".


Professional electricians tend to use a proper test instrument (such as those made by Fluke or Robin) with very good reason.

I know that and thanks for the advice, but I'm not a professional electrician and I was basically using it as an instant double-check as I actually got a shock from the machine. Admittedly, not a very bad one, but enough to feel a tingle.

Remember RCDs are not designed to trip if once ther is a current differential of any magnitude!
The type of RCDs normally used in a domestic installation is only designed operate if the current differential > or = 30mA. In this case the current differential may have been far less, but could still have been enough to give you a fair shock.

I would be very surprised if I'd feel 30mA or if it would light up a 'phase tester' (as crude as it is as a test instrument) to the level that it did.
I can't measure the current flow, but I can at least tell it's enough to be of concern and that I need to isolate the machine from the power by pulling the plug!.

MCBs are over current devices. I am guessing that yours was a 20A B type (as this would be quite typical). It is very likely that the current flowing through the MCB was far, far less which would explain why the unit did not operate.

Yup, I am aware of this, but I am concluding that because there's quite probably no protective earth, that there isn't enough current flowing to trip it.
That's what has me concerned about the lack of earthing.

AFAIK, part of the rational for a protective earth was always to ensure that faults like this would blow a fuse / trip an MCB in the days before RCDs were the norm.

I would strongly suspect that someone's just connected the socket under the sink into the cooker circuit as there's a gas cooker in use, so I would suspect it was 'handy'.


...

I'm not actually intending to tackle this myself. I just want to have my facts straight before I go to the landlord because I do not want any handyman type fixes as it seems like a somewhat more serious situation than a handyman could tackle.

2011

SpaceTime wrote: »

I would be very surprised if I'd feel 30mA

You would! I have had a few nasty "belts" over the years and have yet tripped an RCD (due to receiving a shock). Remember 50mA has the potential to kill hence the 30mA setpoint, so logically far lees than that can really hurt.

or if it would light up a 'phase tester' (as crude as it is as a test instrument) to the level that it did.

They are junk! I have seen then light when connected to earth cables that I can feel no shock from.

I am concluding that because there's quite probably no protective earth, that there isn't enough current flowing to trip it.
That's what has me concerned about the lack of earthing.

I would guess that you are correct, but that does not mean that the test method is sound.

I'm not actually intending to tackle this myself. I just want to have my facts straight before I go to the landlord because I do not want any handyman type fixes as it seems like a somewhat more serious situation than a handyman could tackle.

A very sensible approach in my opinion. Best of luck with it.

SpaceTime

I don't think I'll have any issue, the landlord's extremely sensible and approachable.
I'd say they'll be as concerned as I am.

2011

cerastes wrote: »

I thought 30mA was meant to be quite low?

Yes, low enough not to kill is the design intent.

given a fatal current can be at 80mA-120mA depending on the person and the insulation between them and ground?

I was always told that 50mA had the potential to kill, but that does not mean that up to 30mA would not hurt.

It is possible to get RCDs with a far lower tripping point, but then nuisance tripping can become an issue.

Assuming the dishwasher isn't tripping out an RCD, does this not mean that the circuit it is on, is probably not supplied from an RCD.

That does not necessarily follow.
It could simply be:
1) The current differential was less than 30mA (assuming 30mA type)
2) The RCD was not functioning correctly

cerastes

2011 wrote: »

Yes, low enough not to kill is the design intent.



I was always told that 50mA had the potential to kill, but that does not mean that up to 30mA would not hurt.

It is possible to get RCDs with a far lower tripping point, but then nuisance tripping can become an issue.



That does not necessarily follow.
It could simply be:
1) The current differential was less than 30mA (assuming 30mA type)
2) The RCD was not functioning correctly

You sound like you know more on the subject then me, so it could well be 50mA, I just recal seeing the 80-120mA range mentioned but was told it can vary from person to person. I understood that the 30mA value and the time it took to trip was such that a person wouldn't detect a shock as there is a time factor too. I do my best not to test that, the most Ive ever received was a slight tingle.
I have seen some graphs in the past, but cant remember what they are called, basically that show the performance of RCD's and MCB's.

I think in the OP's situation, the circuit could be correctly protected, but could still have the potential to not trip due to an earth fault because the amount leaking to earth is too low? Id have to dig out old notes to refresh my memory.

Im just wondering why some circuits arent protected by RCD's, my cooker circuit isn't and Ive seen some immersions not on RCD protected circuits, is it because of nuisance tripping?

bassey

Cookers can cause nusiance tripping when protected by an RCD. An immersion should DEFINATELY be protected by an RCD

2011

cerastes wrote: »

so it could well be 50mA, I just recal seeing the 80-120mA range mentioned but was told it can vary from person to person.

50mA sounds pretty small alright. Saying it has "the potential" to be lethal suggests that it would only be lethal under certain (perhaps unique) circumstances.
The values you mentioned are might be more accurate and more likely to guarantee a fatality

See quote from this link:

While any amount of current over 10 mA (.01 amp) is capable of producing painful to severe shock, currents between 100 and 200 mA (.1 - .2 amp) can be lethal.

I understood that the 30mA value and the time it took to trip was such that a person wouldn't detect a shock as there is a time factor too.

Disconnect times (0.4 seconds for circuits up to 32A rating) are to reduce the chances of a more serious injury / death. I would not think that the reason is so that the shock is not felt.

Standard values of operating times for 30mA RCDs (ET101) are:
1) 0.3 sec for a test current of 30mA
2) 0.04 sec for a test current of 250mA


This is a good ETCI link on RCDs

Im just wondering why some circuits arent protected by RCD's, my cooker circuit isn't and Ive seen some immersions not on RCD protected circuits, is it because of nuisance tripping?

Generally fixed appliances do not require RCD protection, there are a few exceptions such as showers (as water & electricity can be a nasty mix).

Although an electrical installation may be completed, tested and certified to a high standard there is always a risk of electric shock from faulty portable appliances being plugged in to a socket outlet. The installation of RCDs mitigates this risk.

If lighting circuits were to have RCDs fitted there is a danger that nuisance tripping could cause loss of lighting, this in itself could lead to a more dangerous situation. Therefore RCDs are generally not fitted to lighting circuits (bathrooms being a notable exception).

Bruthal

SpaceTime wrote: »

I would be very surprised if I'd feel 30mA or if it would light up a 'phase tester' (as crude as it is as a test instrument)

30 mA can give a decent shock alright, I had plenty of shocks that did not trip RCDs, and one or two that did.

The phase tester will never draw 30mA when used. It will be at micro amps level when used by someone not directly in contact with an earth. If the person is in contact with an earth while using a phase tester, the current is still small, but can be perceived. They can be handy for quickly identifying switch wires at a multi gang switch, but they are not great for testing if items are live etc, although they wont light if used on properly earthed washing machines etc, so there is a likelyhood there is an earthing problem at the socket or the socket circuit, plus a fault on that or another machine.

SpaceTime

Fully sorted by an electrician and it was a faulty earth on the socket.

Seems it was just current running off from the Y-capacitors in the power supply for either the variable speed drive for the motor or the electronics that control the machine.