Help with answers not in regs book or in my brain please

[johno999]

Hi All,
Im hoping a bright sparks can help me with one or all of these 3 things that have been foxing me for a while
Any advice appreciated.
Thanks in advance

1) If im not wrong, a type B breaker must activate between 3 & 5 times its rated current within .1 second. There is time/current characteristics charts in regs book. But Im confused why you cant look up what would happen if for example a 32A breaker was to be running on overload at say 50A, as over time this would of course be dangerous.

2) In old days connecting low ohms meter for continuity test to a voltage would damage it. Assuming thats still the case, then does anyone make an r1/r2 test box that plugs in with voltage warning lights on it. As I figure it could be fairly easy to plug in to a live socket in error when doing continuity ring test. Unless of course you turn off the whole board. I could not seem to find such an obvious item for sale, or am I missing something?

3) If I need to do supplementary bonding in a bathroom for one reason or another, i.e no RCD protection. I think im right in saying that all extraneous conductive parts must be bonded to conductive parts. But is this only if they can be touched simultaneously. i.e I have a metal bath & the metal light fitting is at least 2.5 Metres away do I still need to join them with an earth cable?

 

[not clever]

Hi All,
Im hoping a bright sparks can help me with one or all of these 3 things that have been foxing me for a while
Any advice appreciated.
Thanks in advance

1) If im not wrong, a type B breaker must activate between 3 & 5 times its rated current within .1 second. There is time/current characteristics charts in regs book. But Im confused why you cant look up what would happen if for example a 32A breaker was to be running on overload at say 50A, as over time this would of course be dangerous
Errrrm it wouldn't run on OVERLOAD at 50A for any period of time past instantaneous trip time.

2) In old days connecting low ohms meter for continuity test to a voltage would damage it. Assuming thats still the case, then does anyone make an r1/r2 test box that plugs in with voltage warning lights on it. As I figure it could be fairly easy to plug in to a live socket in error when doing continuity ring test. Unless of course you turn off the whole board. I could not seem to find such an obvious item for sale, or am I missing something.
You are definitely missing something, lets start with "safe isolation"

3) If I need to do supplementary bonding in a bathroom for one reason or another, i.e no RCD protection. I think im right in saying that all accessible extraneous conductive parts must be bonded to each circuit protective conductor supplying class1 & class 2 equipment .
i.e I have a metal bath & the metal light fitting is at least 2.5 Metres away do I still need to join them with an earth cable?
701.414.2 is worth a read.

See my comments in red

 

[telectrix]

wot he says ^^^^^. esp 1.and 2.

 

[Pete999]

Wat them 2 said ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

 

[Martyc]

Re: 2, a lot of testers won't let you test if voltage is present or out of range.

 

[PEG]

Also,the time/current graph will give you the information you require,(16.6 minutes),obviously you will have to factor the many variables,such as temperature,age,condition etc.

 

[Deleted member 72666]

Agree entirely with peg re:1. (1000 seconds).

 

[johno999]

Ouch, shot down in flames a little so will try & re phrase it. After doing checks to ensure dead circuit, it would not be impossible to stick your continuity tester into a socket that was supplied from another ring or radial in error, hence my query for an r1/r2 box that also had lights!
And second query was to ask if I was interpreting regs wrong. For example if a light & a bath cannot be simultaneously accessible to touch, i.e at least 2.5 metres apart then do they still have to be bonded together in the event of no RCD, as I cannot understand why it would be necessary. Cheers

 

[Richard Burns]

There is probably a limit to the amount of safety that should be applied to items for professional use as it tends to develop complacency. However the current trend for safety probably means that someone has such a device in pre-production somewhere. However generally multi function testers have in built protection to prevent testing if the circuit is live, so the indication of power present is not required in two places, it is already present in the tester.

The supplementary bonding wording in section 701 for a bathroom does not have the simultaneously accessible qualification that is generally applied to other supplementary bonding. However it does refer to main regulation covering the simultaneously accessible qualification so it may be appropriate.
Certainly the risk is absent if the parts are not simultaneously accessible.
Possibly they might consider that the size of most domestic bathrooms is sufficiently small that with the quantity of plumbing present, as the most likely extraneous conductive parts, would mean that if supplementary bonding were required then the likelihood of there being non simultaneously accessible conductive parts would be sufficiently low that it it would probably mean that someone had missed something and so to cover themselves do not specify this clearly.
Alternatively they were just not thinking about it!

It is notable that for, I think, either swimming pools or agricultural locations they specify that the simultaneously accessible provision is not applicable, which they do not do for bathrooms.

 

[johno999]

Thanks Richard Burns. You have put me on the right track. Wonder if you can help me with one more. I know Im missing something obvious but ... They say the only silly question is the one you dont ask, so at risk of being ridiculed.... Im studying for 2394/5 after being out of game for 10 years. I cant really understand why ZS readings on circuit breakers are important if they are protected by an RCD in the board. The RCD will allow a huge ZS so it seems irrelevant what the breakers will trip at in event of earth fault. If you are anyone can point out where Im going wrong will be appreciated. Many Thanks

 

[Andy78]

Are you talking about RCDs used for fault protection or additional protection ?

 

[johno999]

Hi Andy78, Im just going by the fact that most domestic boards will now have a 30mA RCD which will give fault protection

 

[Andy78]

Hi Andy78, Im just going by the fact that most domestic boards will now have a 30mA RCD which will give fault protection

What sort of earthing arrangement are you talking about, and are you talking about designing new circuits or dealing with high Zs values in existing circuits ?

I would never employ a RCD for fault protection unless there was no other practicable option.

One of the questions I recall from my 2394/5 exam was: Without the use of a 30mA RCD, state 3 methods of making a circuit with high EFLI readings comply with the requirements for disconnection in BS7671.

 

[Brightspark2]

From the ones I've dealt with Older type testers had a quick blow fuse in them. If you connected to a live circuit when on low ohms it would just blow the fuse, not damage it. So you just replaced the fuse.

Newer testers show up with a warning and won't let you test if the circuit is still live.

 

[johno999]

Hi Andy, Like I said Im studying & been out of game for a while, so hope what Im saying makes sense! But, Im guessing that if an RCD of 30mA as mainswitch is in a board then its giving you fault protection whether it was installed for that reason or not. So, if Im testing a circuit attached to a circuit breaker and the ZS is too high for that breaker, then why does it matter so much?