When does voltage drop VD% become a problem for load equipment

[Cartoon1]

I know that we try to stay below 3% voltage drop and 5% for a total from feeder all the way to the branch load. But at what VD% typically will a load start having problem or becomes noticeable to the user?

Motors? for a typical 208-240V rated.
Real loads like heaters, toasters, ovens, general outlets plugins.
Electronic devices like computers and telephone equipment?

Thank you

 

[zbang]

Vague answer to a somewhat vague question-

First, you have to define what problem or noticeable mean here. Heaters will heat more slowly and not get as hot, but for something like a residential oven this probably doesn't matter at all. Most consumer electronics will operate well-enough down to probably 105v and some are rated for 100-240v. A fully-loaded motor might trip the overloads if it runs too long at too low a voltage, but the user might not realize that low voltage is the real problem unless they actually check.

 

[tortuga]

For existing systems I'd say above 10% voltage drop for feeders and branch circuits combined.
For new designs in Florida voltage drop is covered in the 2020 Florida Building Code, Energy Conservation, 7th Edition
C405.5.3 Voltage drop:
"The conductors for feeders and branch circuits combined shall be sized for a maximum of 5 percent voltage drop total."

 

[zbang]

Two separate concerns-
lower voltage operation on the utilization equipment (the OP's question)
energy loss (as heat) in the conductors (which isn't much of a real issue if you're adding heat to the structure anyway)

 

[Jraef]

Also, read this, some of your questions are addressed there.

Voltage Ratings: 110/115/120, 220/230/240 or 440/460/480

This subject comes up a LOT in this and other forums, so I thought it would be a good idea to make it a "Sticky" that can be found and referred to easily when it comes up. There are two "standards" for voltage in North America depending on which END of the wire you are looking at; "Distribution...

forums.mikeholt.com

As to devices that are only resistance heating, what happens with voltage drop is that the heating watts will drop at the square of the voltage change. So for example at 90% of rated voltage, the heating element will only put out 81% of the rated watts (.902). That may or may not be significant. In an oven for example, the heat is thermostat controlled, so all it means is that it will take a little longer for the oven to get to the desired temperature. Similar for a clothes dryer, it just takes longer to dry the clothes. For a hair dryer, it doesn’t get as hot on the various settings, but it’s doubtful that anyone would notice or care.

Electronics is trickier. Most modern electronics have gone to “Switch Mode Power Supplies” (SMPS) and most SMPS are now becoming “auto-ranging” in that they can accept really wide range of input voltage, for expample 100 to 285VAC input is really common now. This is so that they can make one product four use anywhere in the world and only change the plug on the end of the cord. So if you have a 120V power supply for a laptop PC, and your voltage drops to 105V or rises to 130V you would never even know. The problem is, you cannot assume anything, you must read data plates or specs.

Hope that helps.