Ok,
First of all thank you for having me here,
No problem, glad you found us.
I know I can learn a lot of things here.
Judging from just your link you bring a lot to the forum so it works out well.
So my intention with the article was to figure out extremities - surely no one would design or should design a circuit with "maxed-out" load (code would not allow for this),
I can't speak for the CEC but the NEC does alow circuits to be maxed out. I can design a 20 amp circuit with a 20 amp load. I would likely not do that but it could be compliant.
it should be seen as a theoretical calculation just to verify an idea or myth.
In my personal opinion it does not make sense to try to disprove a common practice by setting up extremes that are not common.
For example I could argue cars are unsafe if I say all roads are ice covered at all times.
Now, coming back to the topic, voltage drop depends on couple of things:
- Current
- Length
- Power Factor
- Resistance per unit length
- Inductive Reactance/unit length
Resistance depends on Temp, wire size & material
Reactance depends on Spacing between conductors, diameter, conduit type (magnetic or non magnetic), system frequency
I am pretty confident most here are aware of the above.
Obviously to find exact voltage drop would be complex , but we don't need an exact value
I agree, especially considering that history has shown voltage drop is not really a problem for most equipment.
As I am not an engineer if I was going to calculate VD I would keep it to just this.
Single-phase VD = 2 x K x I x D/CM.
Three-phase VD = 1.732 x K x I x D/CM
More likely I would just use an online VD calculator.
and thats why cable manufacturers provide tables to approximate (quite accurately) these values.
I have never happened to see one of those tables.
I find it strange that engineers recommend this value, the truth is there are so many parameters involved (as mentioned above) one cannot just claim 100ft.
They do it because in the real world it works.
Keep in mind these notes from the engineers are for simple branch circuits. For feeders and services I am sure the EEs are doing calculations.
For this reason at the consulting company I work we size our feeders to compensate for voltage drop - we also note in our spec that the contractor should ensure VD not exceed 3% in a branch circuit.
It sounds like under the CEC that is required, it is not currently required under the NEC.
So if some branch circuits have 2% drop and others have 6% it really does not matter. Equipment is really designed to have a 10% range. Of course that includes utility voltage shortcomings.
Don't get me wrong, a rule of thumb would be great for everyone - it makes everyones lives a whole lot easier, all im saying is if you believe this works prove it.
Hmm, Well under the CEC I guess I would have to prove that I have less than 3% drop on the branch.
Under the NEC I would ask you to prove this rule of thumb does not work.
Maybe this rule works for a very specific scenario - I don't know - If you could post any of the prints that quote this rule that would be great.
Pretty much boiler plate on all our prints, we do large retail and offices.
The notes will often tell us to increase the size of the home run by one size for each 100' of one way length.
Perhaps the EEs found this was easier for electricians to understand and comply with then saying branch circuits must maintain less than X% VD?
