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I am a DIY user trying to understand basic electrical knowledge. I’m not sure if I am in the right place to ask so if not, I’m sorry.

I have an LED display screen (see attached photos)that has 4 power supplies connected together (maybe the term is looped). We are running on 100-120 volts and according to the label each power supply draws 6.8 Amps. I am assuming (and need clarification) that the total load is 27.2 Amps?

If the above is correct (27.2 Amps), does that mean the supply cable (that is connected to the first power supply - e.g main line input) needs to be something like a 30 Amp 10 gauge wire?

Does the wire gauge between each power supply need to be 30 Amp 10 gauge wire or can it reduce in size towards the end power supply?

Also, the blue plastic (PowerCon type) input connector that receives the main line input is only rated for 20 Amps. Doesn’t it need to be 30 Amps???

Any assistance would be most appreciated. Thanks

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1 Answer 1

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Based upon your commentary and the photos the 4 power supplies are connected in parallel to the mains supply. This has been achieved by looping the main power connections to each psu in turn. If the psus individually draw 6.8 A (per label) then the total draw on the mains is 4 x 6.8 = 27.2 A

In theory the looped mains cables are servicing less current e.g. the last cable is only providing 6.8 A to it's psu. You could use a cable with a lower rating but it would cost more to manufacture and would be inherently less tolerant to failure. It makes sense to just using the same cabling spec throughout.

Per the spec on the psus your total draw could be 27.2 A but what it actually is would be dependent on the load e.g. there could be design margin in the psu choice and clearly the psus are a third-party part which met the design criteria. So the Blue 20 A connect might be underspec with regard to the maximum psu load but still ok for the application in question. I would have expected it to be rated at 30 A for safety margin but without more specific design detail one wouldn't know.

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  • \$\begingroup\$ “So the Blue 20 A connect might be underspec with regard to the maximum psu load but still ok for the application in question” - I’m trying to decide if I should risk using the 20 A blue connectors with the possibility of a 30 A load passing through (what would happen if that was the case?) or removing the blue connectors and running the correct size 30 A wire directly to the first power supply. Which would you suggest? \$\endgroup\$
    – uniopp
    Commented Jan 2, 2021 at 13:02
  • \$\begingroup\$ Presumably this is a manufactured unit bought from a supplier. I am not sure why you would want to change it? This would void any warranty on the unit and if the changes are done incorrectly could cause issues. I would not recommend a DIY user modifying the wiring harness. What are you trying to achieve here? \$\endgroup\$
    – mhaselup
    Commented Jan 2, 2021 at 23:45
  • \$\begingroup\$ The first obvious thing to do is to measure the inbound current when the display is in use. Clearly if the current is under 20 A you do not have an issue with the 20 A connector. \$\endgroup\$
    – mhaselup
    Commented Jan 2, 2021 at 23:47
  • \$\begingroup\$ I purchased the display directly from the manufacturer in China and I am dubious as to the standards it was made to and the validity of the warranty. \$\endgroup\$
    – uniopp
    Commented Jan 3, 2021 at 5:04
  • \$\begingroup\$ When I calculated the load at 27.2 A and saw the blue connectors were only rated at 20 A I became concerned. I guess I will just try it as is and see how it goes. What will happen if the load is too much for the blue connectors?? \$\endgroup\$
    – uniopp
    Commented Jan 3, 2021 at 5:13

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