40A shower disconnection time

[oscar21]

Bathroom with an electric shower wired to the latest regs with a 40A MCB and RCD protection. Is the disconnection time 0.4s or 5s.

Looking at the regs it states fixed equipment up to 32A is 0.4s so everything after that unless it has a socket outlet can be 5s, but its a bathroom where everything needs to be RCD protected so surey it needs to be 0.4s.

We are talking about writing a figure on a bit of paper here by the way to satisfy a council bod, not to prevent any sort of injury or death, just a written number. Honestly, I cant wait to retire, it cant come quick enough.

I was previously under the impression that every final circuit now needed to be 0,4s so was surprised to see that stuff over 32A could still be 5s.

 

[loz2754]

5 seconds. Don't second guess yourself! The fact that it's in a bathroom is irrelevant.

On the matter of retiring, I feel your pain. Unfortunately I still have 6 years to go.

 

[oscar21]

5 seconds. Don't second guess yourself! The fact that it's in a bathroom is irrelevant.

On the matter of retiring, I feel your pain. Unfortunately I still have 6 years to go.

Seems stupid to me, a light in a loft that gets used once every 5 years needs to be 0,4 but a shower where you are literally dripping wet and naked can take 5s to disconnect.

Th other thing I've been pulled on is not using the AM2 EICR form, all the ones I've got are the slightly older ones but they are all pre filled in with the 22,000 ticks that need to go in the boxes. Its just a piece of paper, who cares how it looks, the info on it is pretty much the same and no piece of paper has ever saved anyone's life, if something is dangerous then its still dangerous whatever is wrote on the cert.

I really don't know how people put up with jobs that require endless form filling, I walk away from any sort of site work now no matter how good the money is simply because of the paperwork involves, H&S, RAMS, inductions etc etc etc, it could be £10k a week and I'd still say no, just couldn't be arsed with it.

 

[Pretty Mouth]

I guess you're using 3rd party forms? The IET model forms don't actually ask for max permitted disconnection time, so it's not required info. They do ask for max permitted Zs, but you can shove '1667' in there for any RCD protected circuit without giving it a second thought.

I have to agree with you regarding form filling, it's the most tedious part of the job

 

[pc1966]

That is certainly an oddity @oscar21 has uncovered! I was under the assumption that all domestic final circuits were 0.4s or less.

Having said that, for B-curve MCB you don't have the option of meeting 5s and not 0.4s, basically the upper tolerance thermal curve goes down to 5s at around 7*In, so in the B-curve case it will always hit the magnetic trip (and so well below 0.4s) before you can reach 5s.

In ye olde days of fuses, this sudden change would not apply, but maybe then the use of showers > 32A simply did not happen?

It is kind of academic now as they should all be on RCD protection for a shower, but my paranoid streak really likes to see it meet disconnection on the OCPD side as well.

 

[pirate]

I retired from my "proper" job 6 years ago and I was SO glad to rid of the paperwork, form filling and meaningless certification every contract required. I loved my work, but it was ruined by the form-filling. When I started out, our contracts were 2 pages, when I left they were 30 pages, plus we had loads of additional forms added in over the years by our ruling body, by HM Govt. and by statutory changes which placed a huge onus of responsibility on me and my colleagues. All this was to try to shift responsibility from others to us. The anti money laundering paperwork alone was 10 to 20 pages, and the penalties for getting it wrong were severe. Add to that the absolutely horrific PI insurance premiums and excesses and frankly it became an extremely stressful job, even before you actually started on a contract.
In retirement, doing minor electrical jobs, I actually find the completion of the occasional ISITEE paperwork quite enjoyable! (but I couldn't do it every day!)

 

[Dave OCD]

The thing that really gets on my nerves is counting all the 'points' per circuit - tedious !

In terms of a circuit that requires basic or additional protection [depending on the earthing arrangement] by a 30ma RCD then arguably it should disconnect within 300ms ?

 

[davesparks]

Seems stupid to me, a light in a loft that gets used once every 5 years needs to be 0,4 but a shower where you are literally dripping wet and naked can take 5s to disconnect.

What has being wet or naked got to do with it?
That is the reason that it has additional protection by RCD.
If you are waiting for the MCB to disconnect if a wet naked person is receiving a shock then they will be dead at 0.4s. The only difference between 0.4s and 5s will be whether they are cooked rare or well-done.

 

[ipf]

What has being wet or naked got to do with it?
That is the reason that it has additional protection by RCD.
If you are waiting for the MCB to disconnect if a wet naked person is receiving a shock then they will be dead at 0.4s. The only difference between 0.4s and 5s will be whether they are cooked rare or well-done.

The leakage involved whilst peeing oneself, maybe..

 

[oscar21]

What has being wet or naked got to do with it?
That is the reason that it has additional protection by RCD.
If you are waiting for the MCB to disconnect if a wet naked person is receiving a shock then they will be dead at 0.4s. The only difference between 0.4s and 5s will be whether they are cooked rare or well-done.

So why does anything need to disconnect in 0.4s then? Life saving RCDs can trip up to 0.3s, thats only 1/10 slower.

 

[ipf]

So why does anything need to disconnect in 0.4s then? Life saving RCDs can trip up to 0.3s, thats only 1/10 slower.

That's 300 milliseconds not 30.

 

[oscar21]

That's 300 milliseconds not 30.

The max disconnection time of a 30ma RCD is 300ms, which is 0.3 seconds, at x5 or 150ma the max disconnect is 40ms which is 0.04 seconds.

 

[ipf]

The max disconnection time of a 30ma RCD is 300ms, which is 0.3 seconds, at x5 or 150ma the max disconnect is 40ms which is 0.04 seconds.

oops! oscar'd. need me glasses on.

 

[pc1966]

The max disconnection time of a 30ma RCD is 300ms, which is 0.3 seconds, at x5 or 150ma the max disconnect is 40ms which is 0.04 seconds.

Those trip current / time values are intended to keep you in the AC-1 to AC-2 areas, so little risk of fibrillation, of the shock risk model:

Electrical injury - Wikipedia

en.wikipedia.org

The 0.4s standard for TN earthing, and the related 0.2s for TT earthing, follow similar arguments about keeping touch voltage (about U/2 for TN fault as R2 roughly like R1, more or less U for TT) and exposure time during the fault such that typical body resistance won't result in deadly current-time exposure. But that only sort of works for typical dry contact, hence in a bathroom the old (pre-RCD everything) standard for supplementary bonding to further reduce the local voltage differences during a fault.

 

[davesparks]

So why does anything need to disconnect in 0.4s then? Life saving RCDs can trip up to 0.3s, thats only 1/10 slower.

Maybe 1/10 slower but at a vastly different fault current!
The RCD trips at 30mA in 0.3s, that fast enough to save most people from a fatal shock.
The 40A MCB trips at a current in the hundreds of amps in 0.4s

The 0.4s is to keep touch voltages down, prevent damage to cables from long durations of high current faults and that sort of thing.

 

[oscar21]

Maybe 1/10 slower but at a vastly different fault current!
The RCD trips at 30mA in 0.3s, that fast enough to save most people from a fatal shock.
The 40A MCB trips at a current in the hundreds of amps in 0.4s

The 0.4s is to keep touch voltages down, prevent damage to cables from long durations of high current faults and that sort of thing.

That cant be right, the RCD "starts" to trip at 30mA but it depend what bit of the sinewave its at, in 300ms it could be peak voltage and current.

If you've ever had a shock from an RCD protected circuit you'll know it hurts just as much as non RCD, it just doesnt last as long.