Mr Matt
join:2008-01-29
Eustis, FL
kudos:1
1 edit | Circuit breaker rating for generator. If a generator is rated at 30 KW and 36 KVA @ 240 Volts, should the circuit breaker be rated at 125 AMP or 150 AMP? |
|
 LazManPremium
join:2003-03-26
canada | How are you connecting to the gennie?
Typically you size for the conductors/connection device... |
|
| reply to Mr Matt
125A |
|
Mr Matt
join:2008-01-29
Eustis, FL
kudos:1 Reviews:
 ·CenturyLink
 ·Comcast
·Embarq Now Centu..
| reply to LazMan
I have not yet purchased a generator but was looking at the specification of generators, listed by various sellers. If a 30 KW generator, also rated at 36 KVA, is supplied with a 125 AMP circuit breaker, then it would not be possible to utilize the full 36 KVA output into a resistive load. I was also wondering why generators offered by different sellers with the same Kilowatt output rating have different KVA ratings? |
|
|
|
 John GaltForward, MarchPremium
join:2004-09-30
Happy Camp
kudos:5 | reply to Mr Matt
Link to the generator you're considering/have...? |
|
 SmokChsrWho let the magic smoke out?Premium
join:2006-03-17
Saint Augustine, FL
1 edit | reply to Mr Matt
said by Mr Matt:If a 30 KW generator, also rated at 36 KVA, is supplied with a 125 AMP circuit breaker, then it would not be possible to utilize the full 36 KVA output into a resistive load. Perhaps you meant "Reactive" load, if the gennie is 30KW then into a resistive load it's at it's 100% rating at 30KVA into a resistive load. A pure resistive load will have a PF (Power Factor) of 1.00. At a 1.00 PF the KVA = KW.
My recommendation is just stick with the 125A breaker and give the rest little thought. If you are really worried about running it that close to the edge, then you should up size the gennie.
Keep in mind for short duration demands (like and AC starting) the 125A breaker is not going to trip right away. In fact they will typically allow 190A for a full minute and just over 300A for 10 seconds before tripping.
Edit add...
Also if the generator is rated 30KW, that is the max KW you should try to get out of it, regardless of the KVA rating. The KVA rating only comes into play when it is operating into a reactive load with a PF of less than one. IE.. It's a MAX of 30KW and up to 36KVA as long as you don't exceed the true power rating of 30KW. |
|
 leiboldPremium,MVM
join:2002-07-09
Sunnyvale, CA
kudos:6
·SONIC.NET
| reply to Mr Matt
A generator that size may or may not have a single output and breaker that supports the full power of the generator.
Sometimes the full generator power can only be obtained as the sum of multiple loads attached to different generator outlets each with their own breaker.
Fixed generators tend to have a single breaker and terminals for hard wiring to a transfer panel. Portable generators tend to have multiple plug outlets.
When shopping for a generator the breaker and output configuration should definitely be taken into account to ensure it matches the intended usage scenarios.
--
Got some spare cpu cycles ? Join Team Helix or Team Starfire! |
|
Mr Matt
join:2008-01-29
Eustis, FL
kudos:1 Reviews:
·CenturyLink
·Comcast
·Embarq Now Centu..
| reply to John Galt
If I were to go with Propane as a fuel source this would be my first choice:
»www.homestandbygeneratorsystems.···0System/
The advantage the GE system provides is that there are several GE home generator dealers in this area.
If I were to go with Diesel as a fuel source I would consider this generator:
»www.affordablegenerator.com/v/EP···30kw.pdf
The problem with the ALGN30 is that I would have to coordinate the delivery and installation of the generator. |
|
TheMGPremium
join:2007-09-04
Canada
kudos:2 | reply to Mr Matt
A generator rated at 36KVA 240V (36KVA/240V=150A) would need a 150A breaker and suitably rated wiring to utilize the full potential of the generator when running reactive loads (hint: almost everything except heating elements and incandescent lamps). |
|
John GaltForward, MarchPremium
join:2004-09-30
Happy Camp
kudos:5 | reply to Mr Matt
I like the diesel genset...the other, not so much. |
|
| reply to Mr Matt
Hi
Theoretically ; when considering generation systems ; we look only for Reactive Power that is in KVA. Because in real life load is not just Resistive (Heaters etc) . We have fans (Inductive Loads) Compressors and many other such kind of things !
So Consider 36KVA and 240V By this the Breaker Rating can be calculated (36KVA / 240V = 150 A ) That means If your load Reaches 150 A the Breaker has to switch off to save generative and wiring system. what if you Put a CB of 125A instead of 150A .. It will just add an extra safety band to your system. now you can not consume more then 125A but still have i say 20 A left to utilize.
Choose wires which can carry slightly more current then calculated (like e.g 152 A).but strictly not less then this value (value calculated to maximum not Circuit breaker ! because if you plane to increase CB rating a slightly more in future then you will not came up to change whole wiring system ! ) other wise wires would be blown off and the whole system can burst up into Fire.
Regards
--
Regards,
chris |
|
 whizkid3Premium,MVM
join:2002-02-21
Queens, NY
kudos:9 | reply to Mr Matt
said by Mr Matt:If a generator is rated at 30 KW and 36 KVA @ 240 Volts, should the circuit breaker be rated at 125 AMP or 150 AMP?
First instinct would be:
36 kVA / 240V single-phase = 150 amps.
Follow-up points would be: what does the manufacturer say? How is the generator and its windings protected? What type of circuit breaker? What type and size loads will you have? Are they continuous? A thermal-magnetic breaker would have to be 200 amps to allow the generator to provide 36kVA continuously (3 hours). On the other hand, in spite of what you are reading, the generator is unlikely rated to support this.
Another consideration is what can the generator support for fault current? Should you have a short circuit, the generator can only provide so much current for so long, in an attempt to trip the breaker, before it burns up. Proper sizing of the breaker also takes this into account. If all of this is way above your level of expertise or understanding; then use what the manufacturer says; or go with 125A. |
|
SmokChsrWho let the magic smoke out?Premium
join:2006-03-17
Saint Augustine, FL | said by whizkid3:said by Mr Matt:If a generator is rated at 30 KW and 36 KVA @ 240 Volts, should the circuit breaker be rated at 125 AMP or 150 AMP?
First instinct would be: 36 kVA / 240V single-phase = 150 amps. I would still stick with my first thought, For sizing generator protection always go with the lowest rating which is 30KW. Forget that it can do 36KVA and size for the rating of 30KW. Lets not forget that while not likely, the inductive (motors and such) and capacitive (switching power supplies) loads may be close to canceling out. In which case, if you size for the KVA, a full load, will leave you with a roasted generator. So unless the PF has been determined for all the different load variations possible, then the PF should be assumed to be 1.0 and everything else sized accordingly.
Heck I've never been able to trip a 60A breaker feeding my fully electric 2,200 sqft Florida house that has 2, 2 ton AC units.
So I'm not sure what the worry about the 125A is. More than likely if you put a clamp probe onto the service during normal use you would see less than 20A draw on each leg. |
|
