Automatic disconnection of supply

[rich3009]

Can the above method alone be classed as basic protection according to 131.2.1 it can. Based on that regulation you can leave live terminals exposed if supplied by a 30mA RCD

 

[littlespark]

what does 131.2.1 actually say?

Without my BYB at hand, I cant really tell you

 

[Spoon]

Isn't 'basic protection' where you can't touch any live parts by means of barriers, enclosures and things like that.

 

[telectrix]

basically, it says that basic protection can be provided by making sure current can't pass through a body from direct contact with live parts, oe limiting that current to a safe level.

it does not say anywhere in BS7671 that you can have exposed live parts. the above reg. is meant for accidental contact with live parts if. for example, a cover is removed exposing those parts to touch.

 

[rich3009]

I know it's not true but based on that reg alone it states :

Basic Protection
Persons and livestock shall be protected against dangers that may arise from contact with live parts of the installation.

This protection can be achieved by one of the following methods:

1. Preventing a current passing through the body of any person or any livestock
2. Limiting the current which can pass through a body to a non-hazardous valve

Now taking that to the letter without referring to any other regulation an RCD does exactly that, this is a very poorly written regulation and would afford you great defence in court.

 

[telectrix]

but then 416.1 and subsequent regs, apply. you have no defence in court if you complied with 1 reg. and ignored another.

 

[rich3009]

This protection CAN be achieved by one of the following methods:

It doesnt say "ohh and by the way not really" it clearly states you will have achieved basic protection

 

[Risteard]

I know it's not true but based on that reg alone it states :

Basic Protection
Persons and livestock shall be protected against dangers that may arise from contact with live parts of the installation.

This protection can be achieved by one of the following methods:

1. Preventing a current passing through the body of any person or any livestock
2. Limiting the current which can pass through a body to a non-hazardous valve

Now taking that to the letter without referring to any other regulation an RCD does exactly that, this is a very poorly written regulation and would afford you great defence in court.

An RCD most certainly does NOT limit the current. It can't - the current is a product of Ohm's Law. It merely limits the duration if operating correctly.

 

[telectrix]

agree. taking the human bod's resistance as 1K ohm, current is 240/1000 = 240mA. so a 30mA RCD will carry 8 x Idelta n. most RCDs trip at under 10mSec @ x5, so that limits the duration.

 

[rich3009]

Out of scope of the argument, DOES AN RCD provide basic protection down stream

 

[PEG]

I know it's not true but based on that reg alone it states :

Basic Protection
Persons and livestock shall be protected against dangers that may arise from contact with live parts of the installation.

This protection can be achieved by one of the following methods:

1. Preventing a current passing through the body of any person or Limiting the current which can pass through a body to a non-hazardoany livestock
2. us valve

Now taking that to the letter without referring to any other regulation an RCD does exactly that, this is a very poorly written regulation and would afford you great defence in court.

I think you will find that limiting that current/duration,based on a 30mA rcd,will not provide any basic protection to certain members of our livestock community.....only another phone call to the knacker man.

 

[rich3009]

Flawed argument we have either achieved basic protection or we havent, and if we haven't then the regulation 131.2.1 is nonsense

 

[Risteard]

Flawed argument we have either achieved basic protection or we havent, and if we haven't then the regulation 131.2.1 is nonsense

I have already pointed out why you haven't met the requirements of that Regulation with an RCD so how is it flawed?

 

[rich3009]

Because by definition basic protection stops the flow of current and also by definition an RCD provides basic protection regulation 131.2.1 says it does,

 

[rich3009]

I stand corrected if 30mA could be argued is not low enough for livestock .

 

[rich3009]

How about electrical separation can this afford basic protection

 

[rich3009]

.

 

[rich3009]

.

 

[Risteard]

Because by definition basic protection stops the flow of current and also by definition an RCD provides basic protection regulation 131.2.1 says it does,

Where does Regulation 131.2.1 state or even imply that an RCD provides basic protection?

Also I would suggest that basic protection prevents you from coming into contact with live parts as opposed to stopping the flow of current. (We used to refer to it as protection against direct contact.)

 

[rich3009]

Don't get me wrong I totally understand the principle I'm simply pointing out the ambiguity of the regs

 

[Risteard]

How about electrical separation can this afford basic protection

Electrical separation is in no way comparable to an RCD. This gives us two phase conductors with no neutral or Earth reference.

 

[Risteard]

Don't get me wrong I totally understand the principle I'm simply pointing out the ambiguity of the regs

But I don't accept that it is in any way ambiguous. That's why I am asking where precisely you believe that the Regulation in question supports your claim.

 

[Deleted member 26818]

Since when did an RCD limit the current to a non hazardous level?

 

[rich3009]

By time limited fault duration

 

[Risteard]

By time limited fault duration

Limiting the time isn't the same as limiting the current, though, which is what the Regulation stipulates.

 

[Deleted member 26818]

It also won’t limit anything in a short circuit situation.

 

[Wilko]

The title of reg 131.2.1 is : Basic protection (protection against direct contact)
I know I'm simple, but I don't need to think much beyond that do I?

 

[rich3009]

But it states you can achieve it by reducing the current to a non hazardous level I would like to know how, and if an RCD can't do it what can

 

[rich3009]

Why is an RCD designed to detect 30mA there is a reason, because fault currents start at zero and climb in a time curve. And at 30mA we want it off and quick

 

[Risteard]

fault currents start at zero and climb in a time curve

No they don't. Ohm's Law is what you need.

The thermal effects of the fault increase - the fault current is simply a product of the voltage and impedance.

 

[rich3009]

Why do we have a 30ma RCD if the result is a pass through of a massive current, it would make a mockery of it

 

[Amp David]

I know it's not true but based on that reg alone it states :

Basic Protection
Persons and livestock shall be protected against dangers that may arise from contact with live parts of the installation.

This protection can be achieved by one of the following methods:

1. Preventing a current passing through the body of any person or any livestock
2. Limiting the current which can pass through a body to a non-hazardous valve

Now taking that to the letter without referring to any other regulation an RCD does exactly that, this is a very poorly written regulation and would afford you great defence in court.

What would your rcd do if you decided to prod at line and neutral?

 

[Amp David]

I know it's not true but based on that reg alone it states :

Basic Protection
Persons and livestock shall be protected against dangers that may arise from contact with live parts of the installation.

This protection can be achieved by one of the following methods:

1. Preventing a current passing through the body of any person or any livestock
2. Limiting the current which can pass through a body to a non-hazardous valve

Now taking that to the letter without referring to any other regulation an RCD does exactly that, this is a very poorly written regulation and would afford you great defence in court.

What would your rcd do if you decided to prod at line and neutral?

 

[Amp David]

I know it's not true but based on that reg alone it states :

Basic Protection
Persons and livestock shall be protected against dangers that may arise from contact with live parts of the installation.

This protection can be achieved by one of the following methods:

1. Preventing a current passing through the body of any person or any livestock
2. Limiting the current which can pass through a body to a non-hazardous valve

Now taking that to the letter without referring to any other regulation an RCD does exactly that, this is a very poorly written regulation and would afford you great defence in court.

What would your rcd do if you decided to prod at line and neutral?

 

[rich3009]

Depends if you got any leakage to earth, failing that it would do nothing

 

[Risteard]

Why do we have a 30ma RCD if the result is a pass through of a massive current, it would make a mockery of it

It means that it will operate if there is a nominal 30mA earth fault current through it (between 0.5 and 1 times this in reality). So if you were in contact with a phase conductor and 30mA passed through your body it should operate. The 30mA rating has nothing to do with limiting the fault current to 30mA as this would defy Ohm's Law.

 

[Amp David]

Depends if you got any leakage to earth, failing that it would do nothing

Ok lets for the sake of this stupid thread lets presume theres no leakage, except in his y fronts

 

[rich3009]

I see so what's the point of that level, 30mA

 

[rich3009]

Ok lets for the sake of this stupid thread lets presume theres no leakage, except in his y fronts

Fair point no protection

 

[Risteard]

I see so what's the point of that level, 30mA

To protect human life.

It's not about limiting the current to 30mA but ensuring that it operates if 30mA is passing through - well actually 150mA for additional protection to operate within 40mS.

 

[rich3009]

To protect human life.

It's not about limiting the current to 30mA but ensuring that it operates if 30mA is passing through - well actually 150mA for additional protection to operate within 40mS.

But if the result is an instant huge fault current that starts way above that figure why have it, hence my argument that the fault current grows from zero and fast.. In milliseconds; but is nipped in the bud by the RCD before it gets the chance. Plus if your argument is true why doesn't a 500mA protect you.

 

[Spoon]

But if the result is an instant huge fault current that starts way above that figure why have it, hence my argument that the fault current grows from zero and fast.. In milliseconds; but is nipped in the bud by the RCD before it gets the chance. Plus if your argument is true why doesn't a 500mA protect you.

Electrical Safety: The Fatal Current - https://www.physics.ohio-state.edu/~p616/safety/fatal_current.html

 

[rich3009]

The RCD limits the fault current that passes through your body by breaking the fault at 30mA any higher and your in deep

 

[rich3009]

Electrical Safety: The Fatal Current - https://www.physics.ohio-state.edu/~p616/safety/fatal_current.html

Tells me nothing I don't already know

 

[The Ghost]

Must remind myself not to call you if I need electrical work doing.

 

[Deleted member 26818]

30mA RCDs are designed to trip when they detect earth leakage greater than 30mA.
Most will trip below this figure.
So if an RCD detects an earth fault current of 4600A, it will trip, and it will trip within 40ms.
An MCB will also trip if it detects a fault current of 4600A, though it is more likely to trip instantaneously or within 10ms.
Where RCDs are good, is that they will trip at lower currents which an MCB might not trip at, or may take seconds, minutes, hours or even days to trip.

So no, RCDs do not limit fault current, just as fuses and MCBs don’t limit fault current.

 

[rich3009]

Well I would like to know the science behind how it saves your life if it doesn't limit the current your body receives

 

[rich3009]

Explain the fault curve on a fuse chart if earth fault current doesn't grow with time. It shows how long it takes the fault to grow to a large enough magnitude to rupture the fuse. An RCD gets that curve chopped early. But by a means of imbalance measured via earth leakage

 

[rich3009]

Must remind myself not to call you if I need electrical work doing.

Wise because I'm a fireman

 

[Deleted member 26818]

Well I would like to know the science behind how it saves your life if it doesn't limit the current your body receives

Imagine you’re outside mowing your lawn with your hover mower.
The grass is damp, the cable is damp, you accidentally cut through the cable.
You make the mistake of picking up the damp live part of the cable.
You get a belt, you fall down and are unable to release the cable.
Because there’s no CPC in the cable and you’re outside, the fault path is via the general mass of the earth, which in your garden has a high resistance. So high in fact, that there is not enough current to cause the MCB to trip.
You manage to hang on to life for 20 mins, unfortunately it takes your partner 30 mins to wonder what you’re doing and come looking for you.
If there had been a working RCD, the power would have been cut off in 40ms, you’d have got a belt and your arm might ache for the rest of the day.