Published:
9 December 2014
Category:
Trade Talk
Question from Voltimum user: There seems to be a lot of confusion in Australia about the definition of 2 pole RCBO's/MCB's, with some manufacturers incorrectly labelling their 1P+N products as 2 pole. Only a few manufacturers seem to supply real 2 pole RCBO's.
From what I can gather: 1P+N RCBO’s: neutral is not interrupted when the device is tripped, no detection on neutral.
2P RCBO's: switches neutral together with phase. Short circuit & over current detection on both Active & Neutral.
So a 1P+N will interrupt the neutral only if it is manually flipped in the switchboard.
Is the above correct? And if so, it would seem that 2P RCBO's are safer (in the unlikely event of a fault on the Neutral alone).
Any clarification would be greatly appreciated as I have asked three A grade electricians and two electrical engineers, and no-one seems to have the answer.
ANSWER
Thank you for your question and I do understand the confusion.
Unfortunately the standard for RCBO's (AS/NZS 61009) does not provide a definition for the 1P+N and 2P so it is up to manufacturers in their catalogues to provide information.
In the standard there are some definitions we can work with however some manufacturer's catalogues tend to abbreviate this information.
Essentially RCBO's are classified by the number of poles and current paths:-
1P+N Single pole RCBO with one overcurrent protected pole and uninterrupted neutral (two current paths)
1P+N Two pole RCBO with one overcurrent protected pole and an unprotected switched neutral pole
2P Two pole RCBO with two overcurrent protected poles
3P and 4P versions also exist
So a 1P+N device can have either a switched neutral or a solid neutral. Usually the manufacturer’s technical details will clarify this. With a 1P+N (switched neutral) both the active and the neutral will interrupt in the event of a detected fault or operation of the toggle. For a device known as a 1P+N (solid neutral) only the active will be switched in the event of a detected fault or operation of the toggle. Some manufacturers may label a product as 2 pole where they actually mean 2 module (referring to the physical size of the device).
1P+N RCBO's are very popular in both formats (solid neutral and switched neutral). Sometimes the selection depends upon physical size (one module or two modules) and also on cost of the device and the technology of the design. In some situations it is desirable to switch both active and neutral in the event of a fault (some petrochemical applications require this) however common power distribution requirements usually do not specify a switched neutral as mandatory.
To avoid confusion always consult the manufacturers data and if still unclear, speak to the supplier.
I hope this clarifies your question.
Answered by: Ian Richardson, Product Manager - Line Protection, ABB Australia
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