RCD consumer unit and lawnmowers
- Thread starter Speedy471
- Start date
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Yes.
Useful tip - replace the mower flex with 3-core, with the earth connected at the supply end, as you'll have a much better chance of the RCD tripping if you mangle the cable.
Useful tip - replace the mower flex with 3-core, with the earth connected at the supply end, as you'll have a much better chance of the RCD tripping if you mangle the cable.
Are all mowers/garden tools double insulated?
Obviously all circuits protected by that main RCD will go down.
Are there any plugin RCDs which will act faster than the main one, or would you have to replace the main one with a time delayed version (which you obviously wouldn't want to do).
Obviously all circuits protected by that main RCD will go down.
Are there any plugin RCDs which will act faster than the main one, or would you have to replace the main one with a time delayed version (which you obviously wouldn't want to do).
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They have been for years, which is why they'll come with a 2 core cable.
Yup.
Yes and no - you can get in-line 10mA RCDs, possibly plugs, but I've never looked. But there's absolutely no guarantee that one would trip before the upstream one.
More than "not want to" - you may not.
Indeed so. In fact, with a double-insulated tool and 2-core cable, the chances of an RCD fulfilling a useful function are, I would have thought, pretty (or very) low.
Kind Regards, John
They are there in case someone picks up (or comes into contact with) a live severed cable and gets a shock (via themselves and mother earth), it was known as supplementary protection against direct contact in the 16th edn regs which is a lot clearer definition than the 17th edn regs!
A CPC may help in creating a fault path yes.
SY flex with earthed braid would have a better path.
A CPC may help in creating a fault path yes.
SY flex with earthed braid would have a better path.
Yes, I realise that - but it's a fairly unlikely scenario (for a start, only relevant if the OPD does not operate when the cable is severed) and, as far as I can make out (without visiting the 'vanishingly improbable'), just about the only situation in which an RCD would be of any help in relation to such a tool/lead. It is also, IMO, a potentially dangerous approach - since it only comes into play if at least 30mA (possibly a lot more) of current has flowed through a victim. Far better, surely, to insist on measures which increase the chances of a disconnection in response to the cable severing in the first place - as you say ...
If one is going to insist on an RCD, it surely would make much more sense to use the functionality of that RCD to reduce the risk of a current flowing though a human being in the first place (i.e. by also insisting on a CPC or earthed sheath) than to rely only on it limiting the duration for which the current flows through them (which hopefully, but not assuredly, will avoid a fatal outcome).
Kind Regards, John
putting the CPC into the power lead does improve the chances of a protective device operating when the power lead is cut or damaged.
But if the CPC is from a PME source then do not connect it to the frame of the lawn mower as that then becomes an exported PME "earth" with the hazards that can cause.
But if the CPC is from a PME source then do not connect it to the frame of the lawn mower as that then becomes an exported PME "earth" with the hazards that can cause.
Even if it's not PME, it probably would not be advisable to connect the earth to any exposed parts of a double-insulated appliance. No-one has suggested that the appliance end of the CPC (or sheath) should be connected to anything.
Kind Regards, John
So, quite a debatable question! In simple terms then is the main consumer unit RCD not very functional in minimising shock if I mangle the flex and manage to touch the exposed core? Double insulating would mean no risk of shock if touching a the tool itself?
OP - although all the above is good advice please, before you make any further decisions, confirm that the RCD at the consumer unit, covering that circuit, is of a 30mA or 0.03A rating.
There are plenty of installations out there still protected by a 100mA or higher RCD, regardless of incoming earthing system.
There are plenty of installations out there still protected by a 100mA or higher RCD, regardless of incoming earthing system.
That is the one situation in which it would minimise the duration of your shock, and thereby potentially save your life. What it usually won't do, with a 2-core cable, is prevent you getting a shock by touching the exposed mangled end in the first place. That was the basis of BAS's 'tip' - if you had 3-core cable, with the earth connected at the plug end, the RCD would then very probably cut off the power when the mangling happened (before you got a chance to touch it), even if a fuse didn't blow, or an MCB 'trip'. However, although it's theoretically a very good tip, very few people actually do it.
That's correct - unless, of course, the double insulation were to 'fail' in some way (e..g. if the whole tool somehow got 'smashed open').
Kind Regards, John
Actually very possible, quite a few I have repaired in the past have still had the fuses in the plugtops still intact.
Measures which stop people from running over the lead in the first instance are the primary measure such as it contrasting from the grass (bright orange cable), working methods etc. The RCD is there purely as a backup should something happen as I described above.
Or it got very wet and the double insulation was by passed by moisture. In most cases the wet grass and ground would be likely to sink enough current to ground to trip the RCD, but not if the soaking wet mower was moved onto dry concrete, decking or the shed floor.
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