voltage drop for high bay lights

[Stevenfyeager]

Need some advice for someone who doesn't do much commercial work. In a 70 X 100 ft store, we have 20 high bay 160 w fixtures, which do a really nice job.
On one row of 5 lights, we'd like to put on 3 way switch (actually 4 way). But I'm thinking that will affect voltage drop, by adding the 170 feet 12-3 mc between 3 switches. In residential jobs sometimes we use the wireless 3 ways. Thanks !

 

[tom baker]

What voltage?

 

[ptonsparky]

Applied voltage is the biggest question, then how much VD you are willing to accept or are allowed

I used 200' #12 to your first fixture, then 20' to each additional. Total VD to the final fixture was 5.3%. Assumed 120 volt 1.33 amp per fixture.
208 volt is 1.8% VD. .77A/ fixture

 

[Stevenfyeager]

What voltage?

120 v

 

[ptonsparky]

changing to 10/3 MC makes it about 3.7%

 

[synchro]

If most of the cable length would be in a switch loop, then having that switch loop drive the coil of a RIB relay is one option to reduce voltage drop. Could reduce the need for buying more copper.

 

[James L]

How many circuits are you using? How many switches are there currently?

 

[Stevenfyeager]

How many circuits are you using? How many switches are there currently?

it's a new building, I can run 4 circuits for 4 switches for 4 rows of 5 lights each row if I need. Distance of 2 rows together is about 230' of mc #12.
Thanks.

 

[Strathead]

changing to 10/3 MC makes it about 3.7%

And here in Florida, you are limited to 3%

 

[cadpoint]

If most of the cable length would be in a switch loop, then having that switch loop drive the coil of a RIB relay is one option to reduce voltage drop. Could reduce the need for buying more copper.

I'm a box of rocks, why would a RIB change anything about a voltage drop calc?

 

[retirede]

I'm a box of rocks, why would a RIB change anything about a voltage drop calc?

Use the switch that’s 170’ away to switch a relay near the load instead of load current.

 

[synchro]

If most of the cable length would be in a switch loop, then having that switch loop drive the coil of a RIB relay is one option to reduce voltage drop. Could reduce the need for buying more copper.

I'm a box of rocks, why would a RIB change anything about a voltage drop calc?

I see that retirede answered the question concisely, but here's an example:
Say the source and load of a lighting circuit are in relatively close proximity, but there's a switch loop that's hundreds of feet long (perhaps to accommodate several 3 or 4-way switches that are at some distance apart). As a result, there could be a lot of voltage drop if the switch loop conductors carry the full load current. However, contacts in a RIB could could be used to close the circuit between the source and load directly without any of the load current going through the switch loop conductors (they would just need to supply current to the coil of the RIB).

 

[cadpoint]

You gave the box dimensions
You forgot the "Z" travel of your circuit runs, it's got to branch and run from some location/with elevation and that's additional footage
is required for a circuit.

Using Southwire on-line and even dropping down to "current at end of run" of 16A.(which I didn't want to put in) Using 225' as a round number I couldn't get under 8 AWG for less than 3%.run. 220' ain't much better.

Voltage Drop Calculator | Southwire

www.southwire.com

This is all warlock and witchery. I've ever seem them in play, I even wasted 8 minutes watching that guy with a RIB nice enough
to state the wiring technic but only mention of a switch but not where to employ it!

I'm missing, really missing something here...
Thank you just the same...

 

[James L]

I'm a box of rocks, why would a RIB change anything about a voltage drop calc?

Think of the way a garage door opener works.
You power the opener at the ceiling, then have a low voltage switch turning on a relay coil built into the opener.

The controller wiring isn't part of the 120v circuit. Thus, distance matters much less than if you switched the 120v power - especially on 250 ft

 

[curt swartz]

I would never consider running line voltage to add the switch. RIB or we used to frequently use Wattstopper power packs that do the same thing. Then run Class 2 cable to the switch locations.

 

[ptonsparky]

Fill in the: ______ (I used)
Voltage:_______(120)
Distance of BC to first fixture. ____________ (150')
Distance between fixtures. ___________ (20')
BC Amp at:
1st jbox _______(6.7)
2nd______(5.3)
3rd_______(4.)
4th_______(2.7)
5th_______(1.3)

CM OF CONDUCTOR	12​	6,530​		6,530​		6,530​		6,530​		6,530​
LENGTH	150.0​		20.0​		20.0​		20.0​		20.0​
AMPS (MOTOR FLA*1.25)	6.7​		5.3​		4.0​		2.7​		1.3​
1 PH VD	3.941​	116.1​	0.420​	115.6​	0.315​	115.3​	0.210​	115.1​	0.105​	115.0​

Using these #s you are already @ 4.2% VD without the switch loop.

 

[Stevenfyeager]

I would never consider running line voltage to add the switch. RIB or we used to frequently use Wattstopper power packs that do the same thing. Then run Class 2 cable to the switch locations.

Thank you. I've never used RIB or others. How can I learn ?

 

[ptonsparky]

There really isn't much to learn. Google Relay in a Box. Look at one of the PDFs. Use your imagination.

Functional Devices, Inc. Building Automation & Lighting Controls

Functional Devices is the leader in the HVAC, Building Controls, & Energy Management industries for American designed & manufactured devices

www.functionaldevices.com

 

[Stevenfyeager]

I bought this RIB relay RIB01BDC that my supply house recommended but looking on line Functional Devices I'm not sure it is the right one. If it is the right one, I still don't know how to wire it for a 4 way long distance situation. Any help is appreciated. I tried to photo it but it said too big of photo to attach. Thank YOU

 

[Stevenfyeager]

the relay I bought: