News Reports

RCBO misleading information

RCBO "misleading information"

There has been a lot of discussion recently in the press and on-line about RCBOs and, in particular, about the separate earth connection used in some of them.

Unfortunately, a lot of the information that has appeared has been misleading and, in some cases, it is simply wrong.

Given that the recent introduction of the 17th Edition of the IEE Wiring Regulations is resulting in a big increase in the use of RCBOs, we believe that it is important to clarify the situation. One of the most misleading statements is that in order to comply with BS EN 61009, RCBOs must have a separate earth connection. This is not true.

RCBOs are available with no separate earth connection, but which achieve full compliance with the standard.

Another often-made point is that an RCBO without a separate earth connection cannot detect an earth fault if the neutral becomes disconnected. Although true, this is not an issue worthy of consideration. The probability of losing the neutral and having an earth fault at the same time is vanishingly small - so small that there is no need to take it into account when specifying protection devices. In spite of this, many claim that it's still better to use an RCBO with a separate earth connection, "just to be on the safe side". This is not necessarily a good judgement call. This extra connection takes longer to wire, pushing up costs. In addition, some contractors have actually been cutting off the earth wires, which is very bad practice for an RCBO that's been designed and tested on the basis that it will be earthed. Finally, there's the issue of testing. Most manufacturers of RCBOs with earth connections insist that they are removed during insulation testing to avoid possible damage, and during loop testing to eliminate misleading results. Not only does this add more time and cost, there are also other concerns. In particular, the contractor may forget to reconnect the earth wires, leaving the RCBO operating under different conditions from those for which it was designed.

To summarise: claiming that a separate earth connection is essential is not only wrong, it also makes life unnecessarily complicated for contractors by trying to protect against a risk that's theoretical rather than real.

To download a more detailed transcript of this statement from David Pitt, Eaton's Product Marketing Manager for Distribution Products, click on the text below