One reason to not put the RCD at the source is with switch mode power supplies, the background leakage can soon add up to 30mA. Also, if more than one branch is fed, a nuisance trip could occur. Finally, getting someone to reset an RCD can be a pain if it's an electrical cupboard that no one has access to. Conversely some very risk adverse companies would not just want any of their staff resetting a breaker after it had tripped by themselves.
Thinking the the same thing imagine feeding 20 desks with pcs plugged in by one 30 ma rcd, i doubt it would hold in at all given the earth leakage from it equipment. Id go for the rcd sockets or desk mounted inline rcds everytime.
The allowable leakage for a decent switched mode supply is 0.5ma so you are looking at 60 devices... Take an average of 150w per device and you are looking at max power 9kw... You are soo at limit especially as in those environments you should be looking at radials....
One reason to put the RCD into the Consumer Unit is to protect residents of houses and flats if they nail things into walls, such as picture frames, paintings. You would be surprised just how many people do that.
@@timballam3675 A 30mA RCD must trip BY 30mA but may trip FROM 15mA, so that would take the theoretical maximum number of devices leaking 0.5mA down to 30. You'd probably want to allow a not of 'wiggle room' as well, so maybe 20 devices max?
0:36 I love the idea of an RCD requiring a monthly test being buried under a floor and installation like this. Given that furniture layout is flexible and highly likely to cover/trap floor access panels, then you have two problems. 1. It is never going to get a monthly test - ever! 2. If it does trip, then telling the building occupier that they will have to rip out their desks so that the trip can be reset is not going to be popular. Actually my guess would be that an extension lead would be the solution.
If you add a socket to a ring circuit which currently is without RCD protection, do you have to provide RCD protection to the full circuit after the install or is it enough to just protect the socket you have installed with RCD protection? Knowing if the rest of the circuit complies with the need to have an RCD or not it limited where cables are already buried in walls etc.
Depends on the existing system. If it’s domestic, it would be easy enough to swap MCB for RCBO. If you are protecting just a socket, keep in mind it must be type A as standard. I haven’t seen many of those around though.
It is not the case that a higher trip current RCD trips more slowly, so an RCD with a higher trip current than 30mA does not overcome the problem of discrimination/selectivity when multiple RCD's are used.
Have these on all the floor boxes at my work....good fun when some one (namely IT) are plugging/unplugging data and pc's and knock the rcd off with the excess of cable under the floor...makes me 😭 as its myself that has to wrestle the carpet and floor tiles and desks and other sh*te in the wau to flip a breaker back on 😅
@@adriatikkrasniqi1453 No. If there are two RCDs in series from the incoming supply before the consumer unit and the socket outlet, if an earth fault is present on the socket outlet, both RCDs will sense the fault condition and BOTH will react to it. The problem is, you don't know which one is going to trip first, or perhaps both trip. If the RCD in the CU trips then depending on what circuits it is protecting, you are going to lose power to multiple circuits which had selectively been taken into consideration and properly designed in, you would only lose power to the ring main circuit on which the socket is connected, or even only to that socket outlet.
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One reason to not put the RCD at the source is with switch mode power supplies, the background leakage can soon add up to 30mA. Also, if more than one branch is fed, a nuisance trip could occur. Finally, getting someone to reset an RCD can be a pain if it's an electrical cupboard that no one has access to. Conversely some very risk adverse companies would not just want any of their staff resetting a breaker after it had tripped by themselves.
Thinking the the same thing imagine feeding 20 desks with pcs plugged in by one 30 ma rcd, i doubt it would hold in at all given the earth leakage from it equipment.
Id go for the rcd sockets or desk mounted inline rcds everytime.
The allowable leakage for a decent switched mode supply is 0.5ma so you are looking at 60 devices... Take an average of 150w per device and you are looking at max power 9kw... You are soo at limit especially as in those environments you should be looking at radials....
There are different types of RCD for this reason
One reason to put the RCD into the Consumer Unit is to protect residents of houses and flats if they nail things into walls, such as picture frames, paintings.
You would be surprised just how many people do that.
@@timballam3675 A 30mA RCD must trip BY 30mA but may trip FROM 15mA, so that would take the theoretical maximum number of devices leaking 0.5mA down to 30. You'd probably want to allow a not of 'wiggle room' as well, so maybe 20 devices max?
0:36 I love the idea of an RCD requiring a monthly test being buried under a floor and installation like this. Given that furniture layout is flexible and highly likely to cover/trap floor access panels, then you have two problems. 1. It is never going to get a monthly test - ever! 2. If it does trip, then telling the building occupier that they will have to rip out their desks so that the trip can be reset is not going to be popular. Actually my guess would be that an extension lead would be the solution.
Nice explained clear and accurate information. Great video as always Joe👍
Very good well done for explaining this very important topic and we get not understanding this.,
If you add a socket to a ring circuit which currently is without RCD protection, do you have to provide RCD protection to the full circuit after the install or is it enough to just protect the socket you have installed with RCD protection?
Knowing if the rest of the circuit complies with the need to have an RCD or not it limited where cables are already buried in walls etc.
Depends on the existing system. If it’s domestic, it would be easy enough to swap MCB for RCBO. If you are protecting just a socket, keep in mind it must be type A as standard. I haven’t seen many of those around though.
If the supply cable was run in metal trunking to the floor cavity and never buried in a wall could a toughened cable be used instead of armoured?
Yes
What about installing a time delayed or higher trip current rcd (eg 100ma, 300ma) with then a 30ma at the socket?
What he said! 👆
It is not the case that a higher trip current RCD trips more slowly, so an RCD with a higher trip current than 30mA does not overcome the problem of discrimination/selectivity when multiple RCD's are used.
Are you aware of any RCD sockets that have anything other than a 'Type AC' RCD? Surely this would limit their potential efficacy?
The RCD sockets in Legrand / Electrak floor boxes are the A type.
Have these on all the floor boxes at my work....good fun when some one (namely IT) are plugging/unplugging data and pc's and knock the rcd off with the excess of cable under the floor...makes me 😭 as its myself that has to wrestle the carpet and floor tiles and desks and other sh*te in the wau to flip a breaker back on 😅
Why am I seeing RCBOs while we are talking RCDs?
Not to mention that we need to talk about selectivity and such when using RCBOs...
RCBOs and others are part of the RCD family. Like RCCB
Because an RCBO contains an RCD and this video is about options for placement of the RCD, at the consumer unit, at the socket outlet or in-between.
So let's talk about selectivity.
1. Why is it important?
2. How is it achieved?
It only local load should disconnect under fault. Upstream downstream = discrimination achieved…
@@adriatikkrasniqi1453 No. If there are two RCDs in series from the incoming supply before the consumer unit and the socket outlet, if an earth fault is present on the socket outlet, both RCDs will sense the fault condition and BOTH will react to it.
The problem is, you don't know which one is going to trip first, or perhaps both trip.
If the RCD in the CU trips then depending on what circuits it is protecting, you are going to lose power to multiple circuits which had selectively been taken into consideration and properly designed in, you would only lose power to the ring main circuit on which the socket is connected, or even only to that socket outlet.
weirdest shout out to imperial I've heard in a while, not sure I'd be backing their infrastructure that hard