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.