Your take on Arc Flash labeling
Your take on Arc Flash labeling
(OP)
When you have a panel feed directly from an unprotected source (i.e., large transformer secondary) you will generally have a high arc-flash hazard at the incoming lugs of the panel. On an installation such as an I-line (or similar construction), will the selection of the main breaker settings reduce the HRC for the panel or does the entire panel require labeling for the hazard present on the main breaker's source terminals?






RE: Your take on Arc Flash labeling
For switchboards and switchgear with individually-mounted breakers, you might make a case for taking credit for the main breaker for a fault in another section. There's no real test basis for that - just interpretation and common sense (or maybe wishful thinking).
But for group-mounted equipment, I don't believe there is any real debate. Just pretend the main breaker is not there.
RE: Your take on Arc Flash labeling
JIM
RE: Your take on Arc Flash labeling
RE: Your take on Arc Flash labeling
RE: Your take on Arc Flash labeling
You might be able to make a case for taking credit for the main breaker if there was a very substantial and complete enclosure/barrier around the main breaker. But I never seen one in a panelboard or group-mounted switchboard.
One option might be transfer trip: addition of current transformer and relays to allow the upstream primary protection to be shunt-tripped when a fault is detected by the relays.
RE: Your take on Arc Flash labeling
But in a general way, your idea is a sound one at another level. The newest Insulated Case Power Breakers are coming with selectable trip settings so that, for example, you can remotely lower the trip thresholds in order to reduce the Arc-Flash hazard when someone enters an equipment room. While someone is there, the risk of a nuisance trip would be increased, but it often allows testing and simple maintenance or record keeping with a lower level of PPE, i.e. from PPE-4 down to PPE-3.
However for something like an I-Line panel, I doubt there is anything you would be able to do that would lower the risk substantially enough anyway. Low voltage low current systems like where a I-Line would be used already will have relatively low Arc-Flash energy levels to start with. In other words if you are already at a level low enough to allow PPE-2, there is nothing you are going to be able to set on a breaker to get it down to Level 1.
RE: Your take on Arc Flash labeling