It's been a while and I want to make sure I've got this.

[rhamblin]

I need to run four circuits for a break room we are remodelling at work. I want to clarify something, that a coworker disagreed with, and I want to make sure I am understanding correctly. I would like to pull (4) 120 volt circuits into a conduit to feed recepts in the walls. Now if i run 4 circuits (4 hots and 4 neutrals), and 1 ground wire; I have to derate to 70% right (T310.15(B)(3)(a)? But and here is the question, that derating can come off the maximum ampacity in T310.15(B)(16), correct? Since I will be pulling THHN wire into the conduit. I can derate 70% of the 30 amp rated #12 AWG (again using the maximum 90°C column, right? So this derating puts me down to 21 amps, of which I can only use 20 amps because of termination limitations (75°C column).

Am I remembering this correctly?

 

[jap]

Sounds like you pretty well got it figured out.

JAP>

 

[GoldDigger]

The only thing you did not call out in your description is that, if it became an issue, you would have two fewer CCCs to count for derating if you ran two MWBCs instead of four individual circuits.

 

[rhamblin]

The only thing you did not call out in your description is that, if it became an issue, you would have two fewer CCCs to count for derating if you ran two MWBCs instead of four individual circuits.

You used too many abbreviations...CCC’s are current carrying conductors, but what is MWBC’s?

 

[rhamblin]

The only thing you did not call out in your description is that, if it became an issue, you would have two fewer CCCs to count for derating if you ran two MWBCs instead of four individual circuits.

But if I ran multi-wire branch circuits, sharing neutrals, don't I have to put both of them on a double breaker? I wouldn't want someone tripping one breaker to take out two circuits. Am I missing anything here?

 

[charlie b]

You have that right also.

 

[rhamblin]

Another question, there really aren't any limitations to maximum distance between receptacles, are there in non-dwellings? Planning to put them every 12 feet which may be overkill, but the walls are open and I running conduit...There is one wall that they want "beefed" up as there may be crock pots once in a while over there. So maybe 6 feet on center in that area?

 

[JFletcher]

Your first post is spot on.

But if I ran multi-wire branch circuits, sharing neutrals, don't I have to put both of them on a double breaker? I wouldn't want someone tripping one breaker to take out two circuits. Am I missing anything here?

Or use handle ties with 2 1p breakers.

If you're running conduit, there really wont be much extra expense using 2g boxes with 2 duplex receptacles per location. Or every 3' for crock pots - those cords are very short (18"). My West Bend draws 275W, so you could put several of them (5) on a 20A circuit assuming nothing else is on it.

 

[jap]

Another question, there really aren't any limitations to maximum distance between receptacles, are there in non-dwellings? Planning to put them every 12 feet which may be overkill, but the walls are open and I running conduit...There is one wall that they want "beefed" up as there may be crock pots once in a while over there. So maybe 6 feet on center in that area?

You know what your doing.
Pull out the bender and screw gun and rock and roll.

JAP>

 

[kwired]

I need to run four circuits for a break room we are remodelling at work. I want to clarify something, that a coworker disagreed with, and I want to make sure I am understanding correctly. I would like to pull (4) 120 volt circuits into a conduit to feed recepts in the walls. Now if i run 4 circuits (4 hots and 4 neutrals), and 1 ground wire; I have to derate to 70% right (T310.15(B)(3)(a)? But and here is the question, that derating can come off the maximum ampacity in T310.15(B)(16), correct? Since I will be pulling THHN wire into the conduit. I can derate 70% of the 30 amp rated #12 AWG (again using the maximum 90°C column, right? So this derating puts me down to 21 amps, of which I can only use 20 amps because of termination limitations (75°C column).

Am I remembering this correctly?

Actually 75C termination rating is 25 amps for 12 AWG, but then there is 240.4(D), which is referenced in note at bottom of table, which does limit 12 AWG to 20 amps overcurrent protection in your application.

There is no "required receptacles" in this space like there is in most dwelling spaces. Put in as many or as few receptacles as you want.

Crock pots are not too much of a killer on circuit capacity, if people intend to use those large "roaster pans or ovens" that draw 1000+ watts that you better plan one branch circuit for every possible unit.

 

[rhamblin]

Next issue.

Next issue.

We will need to upgrade the 100 amp panel to a 3 phase 120/208V 200 amp panel. We will feed a new transformer Delta-Wye from a Buss duct. So here's my thoughts/calculations. According to my Ugly's book, I'm going to need a 75KVA transformer. According to that, and I can confirm with a calculation, that it will require 90.2 amps on the primary and 208.2 on the secondary.

First question, we need to multiply both of these numbers by 125%, correct? I feel like it normally isn't done, but 215.2 says it does. In my mind, since we don't know what kind of loads will be derived from the panel, we have to assume it could be running continuously.

Therefore the Primary OCPD will be 110 amp fuses in the 200 amp Bus switch.

The only secondary protection will be within 25' of the transformer, which will be the main lug of the panel. I believe this is allowed by 240.21(C)(3). The installation is in a industrial facility. As long as I pull in wire rated for at least 208 amps, (i.e. 4/0 AWG). The Main lug of the panel board will be 200 Amp breaker. And all conductors will be in EMT.

I believe this is also legal via 240.21(C)(6). The ratio of primary to secondary voltage 480/208 is 2.3. Question here when figuring this calculation do we use the phase to ground voltage, or the phase to phase voltage, and how do you know this? Take this ratio and multiply it by 1/3 of 110 amps and we get 84.3 amps. Well my conductors will likely be able to handle 200 amps for the 200 amp panel, so we're good there. Is this the best way to do this, can it be done cheaper?

 

[kwired]

We will need to upgrade the 100 amp panel to a 3 phase 120/208V 200 amp panel. We will feed a new transformer Delta-Wye from a Buss duct. So here's my thoughts/calculations. According to my Ugly's book, I'm going to need a 75KVA transformer. According to that, and I can confirm with a calculation, that it will require 90.2 amps on the primary and 208.2 on the secondary.

First question, we need to multiply both of these numbers by 125%, correct? I feel like it normally isn't done, but 215.2 says it does. In my mind, since we don't know what kind of loads will be derived from the panel, we have to assume it could be running continuously.

Therefore the Primary OCPD will be 110 amp fuses in the 200 amp Bus switch.

The only secondary protection will be within 25' of the transformer, which will be the main lug of the panel. I believe this is allowed by 240.21(C)(3). The installation is in a industrial facility. As long as I pull in wire rated for at least 208 amps, (i.e. 4/0 AWG). The Main lug of the panel board will be 200 Amp breaker. And all conductors will be in EMT.

I believe this is also legal via 240.21(C)(6). The ratio of primary to secondary voltage 480/208 is 2.3. Question here when figuring this calculation do we use the phase to ground voltage, or the phase to phase voltage, and how do you know this? Take this ratio and multiply it by 1/3 of 110 amps and we get 84.3 amps. Well my conductors will likely be able to handle 200 amps for the 200 amp panel, so we're good there. Is this the best way to do this, can it be done cheaper?

90.2 amps is rated primary current. you can protect transformer with 125% in some cases and up to 250% in others.

since you don't have a two wire or a three wire delta secondary you can't protect secondary with the primary device - so you could have up to 250% device on the primary, though I think that would also require 250% for conductor ampacity, so most will still go with 125% as a general rule, which gives you 112.75 for conductor ampacity but can protect it with 125 amp device. Nothing wrong with 90 amp or even less overcurrent device and conductor either - but you may trip if you try to get full capacity out of the transformer.

Secondary protection needs to be 125% maximum of transformer secondary rating, which is 208 amps x 1.25= 260. Note 1 allows next standard size so I believe you could have a 300 amp device on this, though most would never spend more then a 200 amp fuse/ 225 breaker frame size in most instances for no more then would be gained by doing so. Feeder tap rules for secondary conductors will determine needed conductor size here, but in many instances conductor minimum ampacity would need to be equal or greater than overcurrent device setting. That would mean if you went with 300 amp device you need 300 amp conductor also - on something only rated for 208 amps. For general lighting and such nobody will do that, if you are having trouble starting a large motor maybe you might though.

 

[GoldDigger]

But if I ran multi-wire branch circuits, sharing neutrals, don't I have to put both of them on a double breaker? I wouldn't want someone tripping one breaker to take out two circuits. Am I missing anything here?

If the circuit(s) require GFCI or AFCI and you use a model with built-in GF detection you would have to use a double pole breaker and one fault would take out both. If you use non-GFCI single pole breakers with a handle tie, one fault will not take out both, but you will have to turn both off the reset the side that tripped.

 

[kwired]

If the circuit(s) require GFCI or AFCI and you use a model with built-in GF detection you would have to use a double pole breaker and one fault would take out both. If you use non-GFCI single pole breakers with a handle tie, one fault will not take out both, but you will have to turn both off the reset the side that tripped.

I believe this was at his place of work, AFCI probably not a problem, GFCI can be provided at receptacle if needed

 

[rhamblin]

I believe this was at his place of work, AFCI probably not a problem, GFCI can be provided at receptacle if needed

Correct. The receipts will not be close to any sources of water.


Sent from my iPhone using Tapatalk

 

[rhamblin]

First question, we need to multiply both of these numbers by 125%, correct? I feel like it normally isn't done, but 215.2 says it does. In my mind, since we don't know what kind of loads will be derived from the panel, we have to assume it could be running continuously.

You can protect transformer with 125% in some cases and up to 250%

So, are we required to size it based on continuous use? Furthermore, what is the wire between the buss switch and the xfmr? I assume its a feeder, but since it feeds a separately derived system, does that make it a branch circuit?

 

[rhamblin]

Secondary protection needs to be 125% maximum of transformer secondary rating, which is 208 amps x 1.25= 260. Note 1 allows next standard size so I believe you could have a 300 amp device on this, though most would never spend more then a 200 amp fuse/ 225 breaker frame size in most instances for no more then would be gained by doing so. Feeder tap rules for secondary conductors will determine needed conductor size here, but in many instances conductor minimum ampacity would need to be equal or greater than overcurrent device setting.

I plan to use a 200 amp breaker in the panelboard. So then the question becomes, can I use 3/0 AWG (rated 200 amps at 75°C) or do I need to increase by 125% for the possibility of continuous duty (125% x 200 amps = 250 amps, 250KCMIL AWG).
I don't believe I have to because of 215.2(A)(1)(exception No. 1).
Thoughts? I just want to make sure I am doing this correct and remembering it correctly.

 

[jumper]

So, are we required to size it based on continuous use? Furthermore, what is the wire between the buss switch and the xfmr? I assume its a feeder, but since it feeds a separately derived system, does that make it a branch circuit?

The tranny is built to be run at 100% of continuous loads and non continuous loads. You do not need to upsize.

The 125% kwired is talking about is for Primary protection of the tranny.

Both input and output conductors for the tranny are feeders.

Conductors must be sized with continuous loads called at 125% plus Non continuous at 100%.

Good link on tranny install,

https://www.mikeholt.com/mojonewsarchive/NEC-HTML/HTML/TransformerInstallation~20020516.htm

 

[GoldDigger]

So, are we required to size it based on continuous use? Furthermore, what is the wire between the buss switch and the xfmr? I assume its a feeder, but since it feeds a separately derived system, does that make it a branch circuit?

Since a branch circuit starts at the last overcurrent device and ends at the point of utilization of the power (the outlet where power is taken from the building wire system to a load), the term does not apply to the feed to an SDS, even if the far side of the SDS goes to a single outlet.
There will be OCPD on the secondary side of the transformer even if the transformer itself is considered to be protected by primary OCPD alone.
JMO.

Sent from my XT1585 using Tapatalk

 

[rhamblin]

Good link on tranny install,

https://www.mikeholt.com/mojonewsarchive/NEC-HTML/HTML/TransformerInstallation~20020516.htm

so I’ll be installing 350 KCMIL conductors for a 200 amp panel, that doesn’t seem right, does it?