Type AC RCD vs type A RCD

baby fish

just doing little bit of research online and have found there is type *AC rcd* and type *A rcd* usually found in domestic situation

So I have type AC rcd in my house.

Are type AC still being installed these days?
Any need to upgrade to type A rcd?

Risteard81

There are actually A, B and AC types.

Basically a Type A RCD is also sensitive to pulsating DC currents which would disable a Type AC RCD.

Type AC RCDs generally only seems to be used in the UK these days so perhaps it was purchased online or something?

baby fish

The AC type,its in house I suppose 5 - 7 years, doubt it was bought in UK.

I presume at some stage AC type was what was used in Ireland? When did the A type become the norm to use?

Is the AC type considered safe to continue using in a house?

Thanks

Gashmuncher

Type AC RCDs as the name suggests protect only against AC fault currents. A lot of modern equipment and applicances particularly those containing motors which require speed control now use triacs to chop the AC sine wave and create a DC supply. This DC is then used to drive DC motors which are then more easily controlled.
It was discovered that if an earth fault occurred on the DC circuits, the AC type RCD could not detect it and therefore would not trip. This prompted the necessity to develop A type RCDs which are designed to detect both AC and DC fault currents.
The 2008 4th edition of the wiring rules ET101 states in rule 531.2.3.3. that type AC RCDs should not be used to protect equipment that produce " Residual Pulsating Currents"
To answer the posters original question, If he wants to comply with the current wiring rules (4th edition 2008) and he has equipment that produces residual pulsating currents he needs to replace his Type AC RCDs with Type A.

For lots of information regarding RCDs see. http://www.etci.ie/docs/ET214.pdf

baby fish

Gashmuncher wrote: »

lots of information regarding RCDs see. http://www.etci.ie/docs/ET214.pdf

Thanks, combined - your post and link explain a lot!!

I had actually read the linked file prior to posting but it didn't fully make sense, have read it again now things are bit clearer now, probably still a few gaps in my understanding...I have a few more questions if you could answer

1. From the linked file section 6 : "arrangements should also be made for regular testing by application of an external residual current". What is this test?

2. You mentioned not being able to detect an Earth fault is the problem with type AC, What combination of wires touching causes an earth fault, or how would an earth fault come about, does the test above create an Earth fault?

3. from what you have posted and the linked file: 5.2 Installation & Load Characteristics , Type of load, e.g. AC load only or load containing rectification or power control
devices. [/B].....If I looked at an appliance ( e.g. a food blender) or a power tool (power drill, skill saw) or a light (LED) or a motor ( 1kw ) is there a symbol to say it converts AC or DC ?

Gashmuncher

baby fish wrote: »

Thanks, combined - your post and link explain a

1. From the linked file section 6 : "arrangements should also be made for regular testing by application of an external residual current". What is this test?

2. You mentioned not being able to detect an Earth fault is the problem with type AC, What combination of wires touching causes an earth fault, or how would an earth fault come about, does the test above create an Earth fault?

3. from what you have posted and the linked file: 5.2 Installation & Load Characteristics , Type of load, e.g. AC load only or load containing rectification or power control
devices. [/B].....If I looked at an appliance ( e.g. a food blender) or a power tool (power drill, skill saw) or a light (LED) or a motor ( 1kw ) is there a symbol to say it converts AC or DC ?

1. The test actually creates an earth fault and therefore an unbalances the current between live and neutral. The test device measures the time in milliseconds between when the fault occurs and when the RCD disconnects. These times are required to be within the parameters set by Annex 61G of ET101 4th Edition. The requirements are, that at 1/2 the RCD rated current the RCD should not trip. (eg. for a 30ma RCD 15ma) At X1 the RCD rated current the RCD should trip in 300ms or less (eg. for a 30ma RCD 30ma), at X5 the RCD rated current the RCD should trip in 40ms or less (eg. for a 30 ma RCD 150ma)
The test is done with a standard electricians tester like the megger or fluke multi tester. It is a requirement that all registered electricians have this tester. (Unfortunately most do not know how to operate the tester correctly)

2. Live or Neutral or Positive or Negitive conductors coming into contact with earth will provide an alternative route for the current back to the supply point and therefore create an earth fault.

3. The symbol for an A type RCD is Rectangle with a sine wave in it and also a straight line and dashed line indicating the device detects both AC and Pulsed DC fault currents. I have seen domestic applicances with a sticker on them advising that the appliance needs to be protected by an A type RCD.