Following on from a recent discussion that moved slightly off topic and into the pros & cons of isolation transformers, I thought I would start a separate learned discussion
So, the scenario :
A temporary outside decoration is to consist of a 20m length of festoon cabling with 40 coloured LED BC lamps. This a 230V powered festoon intended to be powered from the mains. This festoon string has only two cores in its mains lead - it does not have an earth core & has no provision for any kind of earthing.
Lets consider the possible supply arrangements:
i). Plug directly into the nearest available 13A socket (which may or may not have RCD protection).
ii). Plug into the nearest 13A socket via a plug-in type 30mA RCD (which may in addition to any permanently installed RCD).
iii). Power from an 'isolation transformer'. Here is were the discussion really starts. This transformer may have a number of possible configurations:
a). Full floating - the secondary has no connection to earth.
b). Connected to the mains earth - one leg of the secondary is connected to the installation earth (which may be PME or TT).
c). Connected to an independent earth rod - one leg of the secondary is connected to a separately driven copper earth rod (lets assume, for the purpose of discussion, it is well clear of any other buried metalwork which maybe connected to a PME system).
Any of the above three transformer configurations may be used with a plug-in type RCD on the secondary side (or primary side.....)
Please note: this is a topic for learned discussion, I'm not asking for advice on how to do this, I'm starting a discussion
Over to you, Gentlemen!
So, the scenario :
A temporary outside decoration is to consist of a 20m length of festoon cabling with 40 coloured LED BC lamps. This a 230V powered festoon intended to be powered from the mains. This festoon string has only two cores in its mains lead - it does not have an earth core & has no provision for any kind of earthing.
Lets consider the possible supply arrangements:
i). Plug directly into the nearest available 13A socket (which may or may not have RCD protection).
ii). Plug into the nearest 13A socket via a plug-in type 30mA RCD (which may in addition to any permanently installed RCD).
iii). Power from an 'isolation transformer'. Here is were the discussion really starts. This transformer may have a number of possible configurations:
a). Full floating - the secondary has no connection to earth.
b). Connected to the mains earth - one leg of the secondary is connected to the installation earth (which may be PME or TT).
c). Connected to an independent earth rod - one leg of the secondary is connected to a separately driven copper earth rod (lets assume, for the purpose of discussion, it is well clear of any other buried metalwork which maybe connected to a PME system).
Any of the above three transformer configurations may be used with a plug-in type RCD on the secondary side (or primary side.....)
Please note: this is a topic for learned discussion, I'm not asking for advice on how to do this, I'm starting a discussion
Over to you, Gentlemen!