My mates's house is an old one with the inevitable modified electrics !

The garage (free standing) and a room under the stairs share a modern CU with 2 16A MCB's and a normal 30mA RCD. The room under the stairs is the home office so contains the PC, printer and router.

I rewired the garage for him some years back including converting an old wood turning lathe (Graduate) to run off a 3 phase inverter. It's here that the oddity occurs. Bob reported back to me some time ago that on occasions when shutting down the workshop at then end of the day the RCD tripped - and I was pinned down today to investigate. And of course nothing happened !

Bob's normal procedure when shutting up for the evening is to switch off the 2 150W halogen floodlights he uses for lighting the lathe and then powering off the inverter (a small 1.5kW one) at the 13A socket. As is the way of things, this sequence sometimes gets reversed and erratically it's then that the trip occurs - ie the inverter gets switched off before the floodlights, and then boof! he's in the dark as the RCD in house front hall has tripped.

The usual suspect of earth leakage current is clearly the culprit, but why on switching **off** the just somewhat larger than domestically normal SMPS ? Or is one of the floodlights leaking and the switch off just creates that little bit of instability on the circuit ? If the latter, is there any way of measuring it ?

Thanks
Rob

On 06/01/2014 20:24, robgraham wrote:

The usual suspect of earth leakage current is clearly the culprit,
but why on switching **off** the just somewhat larger than
domestically normal SMPS ? Or is one of the floodlights leaking and
the switch off just creates that little bit of instability on the
circuit ? If the latter, is there any way of measuring it ?

If the RCD is sensitised close to its tripping point in normal
operation, then any transient can be enough to push it over the edge...

Might be worth adding a known quantity of leakage yourself and seeing at
what point it trips. A RCD tester with a ramp facility is handy for that.

--
Cheers,

John.

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John Rumm wrote:
On 06/01/2014 20:24, robgraham wrote:

The usual suspect of earth leakage current is clearly the culprit,
but why on switching **off** the just somewhat larger than
domestically normal SMPS ? Or is one of the floodlights leaking and
the switch off just creates that little bit of instability on the
circuit ? If the latter, is there any way of measuring it ?

If the RCD is sensitised close to its tripping point in normal
operation, then any transient can be enough to push it over the edge...

Might be worth adding a known quantity of leakage yourself and seeing at
what point it trips. A RCD tester with a ramp facility is handy for that.

I expect the inverter is only having its live connection switched
leaving half the internal filter connected to neutral and earth

My mates's house is an old one with the inevitable modified electrics !

The garage (free standing) and a room under the stairs share a modern CU
with 2 16A MCB's and a normal 30mA RCD. The room under the stairs is the
home office so contains the PC, printer and router.

I rewired the garage for him some years back including converting an old
wood turning lathe (Graduate) to run off a 3 phase inverter. It's here
that the oddity occurs. Bob reported back to me some time ago that on
occasions when shutting down the workshop at then end of the day the RCD
tripped - and I was pinned down today to investigate. And of course
nothing happened !

Bob's normal procedure when shutting up for the evening is to switch off
the 2 150W halogen floodlights he uses for lighting the lathe and then
powering off the inverter (a small 1.5kW one) at the 13A socket. As is
the way of things, this sequence sometimes gets reversed and erratically
it's then that the trip occurs - ie the inverter gets switched off before
the floodlights, and then boof! he's in the dark as the RCD in house front
hall has tripped.

The usual suspect of earth leakage current is clearly the culprit, but why
on switching **off** the just somewhat larger than domestically normal
SMPS ? Or is one of the floodlights leaking and the switch off just
creates that little bit of instability on the circuit ? If the latter,
is there any way of measuring it ?

Thanks
Rob


I had persistent rcd trips when turning off a set of uplighters with folded
fluorescent lamps. Totally solved the issue by putting a snubber circuit
(capacitor in series with a resistor) across the load

Andrew

On Monday, January 6, 2014 10:02:50 PM UTC, Andrew Mawson wrote:
My mates's house is an old one with the inevitable modified electrics !



The garage (free standing) and a room under the stairs share a modern CU

with 2 16A MCB's and a normal 30mA RCD. The room under the stairs is the

home office so contains the PC, printer and router.



I rewired the garage for him some years back including converting an old

wood turning lathe (Graduate) to run off a 3 phase inverter. It's here

that the oddity occurs. Bob reported back to me some time ago that on

occasions when shutting down the workshop at then end of the day the RCD

tripped - and I was pinned down today to investigate. And of course

nothing happened !



Bob's normal procedure when shutting up for the evening is to switch off

the 2 150W halogen floodlights he uses for lighting the lathe and then

powering off the inverter (a small 1.5kW one) at the 13A socket. As is

the way of things, this sequence sometimes gets reversed and erratically

it's then that the trip occurs - ie the inverter gets switched off before

the floodlights, and then boof! he's in the dark as the RCD in house front

hall has tripped.



The usual suspect of earth leakage current is clearly the culprit, but why

on switching **off** the just somewhat larger than domestically normal

SMPS ? Or is one of the floodlights leaking and the switch off just

creates that little bit of instability on the circuit ? If the latter,

is there any way of measuring it ?



Thanks

Rob





I had persistent rcd trips when turning off a set of uplighters with folded

fluorescent lamps. Totally solved the issue by putting a snubber circuit

(capacitor in series with a resistor) across the load



Andrew

The professionalism here is beyond my limited grasp of electrics but this thread may hold the answer to a problem we have. Something in the kitchen ring occasionally trips the rcd.(Never when I'm around) SWMBO is convinced its the fridge but then she's looking for a new one. I was just this morning wondering if there was any device I could place between the fridge and the socket to help me prove/disprove her theory.

We had a similar problem many years ago which resulted in the replacement of many toasters, as the assumed culprits, and the splitting of the ring in an effort to source the problem. It transpired that the main connection to the house was faulty. It eventually melted the connection and damn near caused a fire.

I did talk it through with an electrician we had in to wire some 3 phase sockets in the factory but he had no suggestions and as the house is 30 miles away from the factory and his rates were a bit eye watering I didn't fancy paying him for 2 hours travelling time and two hours head scratching.

So even if I had enough knowledge to allow me talk the suggestions through with someone it would be a big help

In article , fred
wrote:

[Snip]

The professionalism here is beyond my limited grasp of electrics but this
thread may hold the answer to a problem we have. Something in the kitchen
ring occasionally trips the rcd.(Never when I'm around) SWMBO is
convinced its the fridge but then she's looking for a new one. I was just
this morning wondering if there was any device I could place between the
fridge and the socket to help me prove/disprove her theory.

We had a similar problem many years ago which resulted in the replacement
of many toasters, as the assumed culprits, and the splitting of the ring
in an effort to source the problem. It transpired that the main
connection to the house was faulty. It eventually melted the connection
and damn near caused a fire.

[Snip]

My initial suspect would be an electric kettle.

--
From KT24

Using a RISC OS computer running v5.18

On Tuesday, January 7, 2014 9:16:51 AM UTC, charles wrote:
In article , fred

wrote:



[Snip]



The professionalism here is beyond my limited grasp of electrics but this

thread may hold the answer to a problem we have. Something in the kitchen

ring occasionally trips the rcd.(Never when I'm around) SWMBO is

convinced its the fridge but then she's looking for a new one. I was just

this morning wondering if there was any device I could place between the

fridge and the socket to help me prove/disprove her theory.



We had a similar problem many years ago which resulted in the replacement

of many toasters, as the assumed culprits, and the splitting of the ring

in an effort to source the problem. It transpired that the main

connection to the house was faulty. It eventually melted the connection

and damn near caused a fire.



[Snip]



My initial suspect would be an electric kettle.



--

From KT24



Using a RISC OS computer running v5.18

Strange you should say that. She has just replaced the second Dualit kettle to fail. (They make good toasters but their kettles are sh**e). The second one ? Yes. It was the right colour for the kitchen, you see. This time common sense prevailed and a Cuisinart purchased.

Wonder if that was the cause.

Only time will tell.

Thanks for your tip. It has given me a bit of ammunition

In article ,
fred writes:
The professionalism here is beyond my limited grasp of electrics but this thread may hold the answer to a problem we have. Something in the kitchen ring occasionally trips the rcd.(Never when I'm around) SWMBO is convinced its the fridge but then she's looking for a new one. I was just this morning wondering if there was any device I could place between the fridge and the socket to help me prove/disprove her theory.

Use an extension lead to plug the fridge into a different circuit,
if you have another circuit which is on a different RCD.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

On Tuesday, January 7, 2014 12:24:44 PM UTC, Andrew Gabriel wrote:
In article ,

fred writes:

The professionalism here is beyond my limited grasp of electrics but this thread may hold the answer to a problem we have. Something in the kitchen ring occasionally trips the rcd.(Never when I'm around) SWMBO is convinced its the fridge but then she's looking for a new one. I was just this morning wondering if there was any device I could place between the fridge and the socket to help me prove/disprove her theory.



Use an extension lead to plug the fridge into a different circuit,

if you have another circuit which is on a different RCD.



--

Andrew Gabriel

[email address is not usable -- followup in the newsgroup]

Except it only occurs occasionally and I cant see her-indoors living with an extension lead snaking around her kitchen for weeks on end.

fred wrote:
On Tuesday, January 7, 2014 12:24:44 PM UTC, Andrew Gabriel wrote:
In article ,

fred writes:

The professionalism here is beyond my limited grasp of electrics but this thread may hold the answer to a problem we have. Something in the kitchen ring occasionally trips the rcd.(Never when I'm around) SWMBO is convinced its the fridge but then she's looking for a new one. I was just this morning wondering if there was any device I could place between the fridge and the socket to help me prove/disprove her theory.



Use an extension lead to plug the fridge into a different circuit,

if you have another circuit which is on a different RCD.



--

Andrew Gabriel

[email address is not usable -- followup in the newsgroup]

Except it only occurs occasionally and I cant see her-indoors living with an extension lead snaking around her kitchen for weeks on end.

Her indoors needs to understand that analysis of some problems need some
tolerance on her part!
Are you man or mouse in your house?

On 07/01/2014 09:01, fred wrote:

The professionalism here is beyond my limited grasp of electrics but
this thread may hold the answer to a problem we have. Something in
the kitchen ring occasionally trips the rcd.(Never when I'm around)
SWMBO is convinced its the fridge but then she's looking for a new
one. I was just this morning wondering if there was any device I
could place between the fridge and the socket to help me
prove/disprove her theory.

I would first point you at:

http://wiki.diyfaq.org.uk/index.php?...Nuisance_trips

We had a similar problem many years ago which resulted in the
replacement of many toasters, as the assumed culprits, and the
splitting of the ring in an effort to source the problem. It
transpired that the main connection to the house was faulty. It
eventually melted the connection and damn near caused a fire.

The combination of transients and mains input filters seems to be a bad
one for RCDs - they are often either fast enough or "upset enough" to
see the imbalance caused by the filters dumping excess harmonic noise to
earth.

I did talk it through with an electrician we had in to wire some 3
phase sockets in the factory but he had no suggestions and as the
house is 30 miles away from the factory and his rates were a bit eye
watering I didn't fancy paying him for 2 hours travelling time and
two hours head scratching.

So even if I had enough knowledge to allow me talk the suggestions
through with someone it would be a big help

There is quite a lot of detail in the wiki that should be doable even
with basic test gear, and a methodical approach.

--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/