A search on "daisy chaining
power strips" or anything like that will find plenty of discussions on the topic but the general concept is that due to increasing problems in offices, dorm rooms,
etc., a few years ago the
NEC and UL clarified some issues related to
power strips or "relocatable
power taps" and defined that these devices are intended to be used on a temporary (less than 90 day) basis, plugged directly into an
outlet (not into an extension
cord or another
power strip) and not permanently mounted. Many of the same issues apply to extension cords, e.g. you should not
daisy chain extension cords or use them for 'permanent' wiring. You also typically want to avoid placing multiple
MOV based surge suppression devices in series.
Devices that are hardwired rather than terminated with a
plug and 'permanently' mounted inerently limit the load and are not relocatable and thus do not fall under the same categories. However, devices that are designed to be rack or furniture mounted but that connect to a
receptacle via a
plug do seem to potentially be considered the same, it is the
plug that in
effect makes the device relocatable and many of the same concerns still apply. For example, a sequencer may only have two outlets per 'step' but the ratings and potential load for the
unit is dependent upon the potentially connected devices so it is the total number of receptacles on the device and the 'typical' load those represent that is the concern.
Keep in mind that all of these issues relate to the potential conditions represented by the devices and not to the actual loads or conditions. It does not matter that you only have some minimal load currently plugged in to a
power strip, it is the potential load represented should 'typical' devices be plugged in to all of the outlets on the device. Perhaps a simple way to look at it is that if you
plug a 15A rated
power strip into a 15A rated sequencer which is plugged into a 15A
receptacle, based on 'typical' loads and the device ratings, you have connected a potential 30A load to a 15A device and that to a 15A
receptacle. That you may have less than 15A of load currently on everything does not matter, the configuration based on the devices as rated represents a potential danger.
I can say that when these changes occurred it significantly changed the way I design the
power distribution within racks and systems. In some cases it simply means something as simple as having a duplex
outlet to directly
power two distribution devices rather than daisy chaining the two devices to a single
receptacle. But in more complex systems it can mean a lot more thought and careful
layout of how everything is powered.
By "punched" I meant an inspection identifying it as an item to be addressed or a violation. It seems that these particular issues have become a focus for many Fire Marshals.