Diverted Neutral Current - Description Overview Part 1

The video begins with an introduction to the concept of diverted neutral current, explaining that it refers to current which would normally flow in the neutral conductor but is instead directed elsewhere. The speaker, JW, clarifies that this phenomenon occurs outside of individual electrical installations, such as buildings, and is due to issues within the supply network itself. The potential dangers of such diverted current are highlighted, emphasizing the importance of understanding how these situations arise and what to look for to ensure safety. JW also previews the content of the next video, which will include a demonstration using a test rig to simulate various scenarios involving diverted neutral current.

This paragraph delves into the specifics of TNCS (Terra Neutral Combined with Earth and Screen) systems, which are common in the UK and many other places. The speaker explains the setup of TNCS, where a single conductor serves as both the neutral and Earth conductor. The paragraph discusses how in normal operation, current may naturally be diverted through extraneous conductive parts like water or gas pipes, which are bonded to the main earthing terminal to maintain equal potential. The speaker also addresses the potential for current to flow through bonding conductors even when an installation is isolated, due to parallel paths created by adjacent properties sharing metallic parts.

The speaker further explores the behavior of current in TNCS systems, particularly when there are multiple paths for current to return. He explains that the presence of a bonding conductor to a shared metallic part like a pipe can result in a分流 of current, with some of it traveling through the pipe and into the ground. This is a normal occurrence in TNCS systems and does not indicate a fault. The speaker also discusses the implications of a broken or disconnected neutral and Earth conductor, which could lead to current being diverted through other paths and potentially causing issues in adjacent properties.

In this paragraph, the speaker advises on safe practices when working with electrical installations that may have diverted neutral current. He emphasizes the importance of first disconnecting the supply and using a clamp meter to check for current on bonding conductors before making any alterations. The presence of current could indicate a problem within the supply network, and the speaker warns that disconnecting a bonding conductor could result in a dangerous voltage if there is an open combined neutral and Earth conductor elsewhere in the network. The speaker stresses the need to check for voltage after disconnecting any bonding or earthing conductors to ensure safety.

The speaker discusses the rare but serious issue of open CNA (Combined Neutral and Earth) conductors, which can pose significant safety risks. He explains that while such occurrences are not common, they do happen and must be taken seriously. The speaker advises using a clamp meter to measure any current on bonding or earthing conductors and a single pole voltage indicator to check for voltage after disconnecting these conductors. He warns that any significant voltage detected could indicate a major problem and the need to call in professionals to investigate the network. The speaker concludes by reiterating the importance of safety measures and the potential dangers of diverted neutral current.