RFS/MOCP
- Thread starter rose1981
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luckylerado
Senior Member
- Location
- Lake of the Ozarks
Recommended Fuse Size
Thanks.
IMO, we would need to know the MCA to apply 440.12.
Odd nameplate to have MOCP ratings of 42/38. European possibly ?
victor.cherkashi
Senior Member
- Location
- NYC, NY
victor.cherkashi
Senior Member
- Location
- NYC, NY
If manufacturer specify maximum recommended fuse size, he did work for us by calculating fuse per section 440.* i have other question:*
I read in some forum that reads: if nameplate doesn't specify the recommended size of c.b. it means manufacture didn't test the equipment with branch c.b. and we cannot use C.B. for branch circuit. what is your opinion for using HACR C.B. for branch circuit if manufacturer indicates only fuse size on his nameplate?*
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I read in some forum that reads: if nameplate doesn't specify the recommended size of c.b. it means manufacture didn't test the equipment with branch c.b. and we cannot use C.B. for branch circuit. what is your opinion for using HACR C.B. for branch circuit if manufacturer indicates only fuse size on his nameplate?*
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- Location
- Massachusetts
In my opinion that would be a violation.
As a side note, most, if not all molded case breakers are now HACR.
http://static.schneider-electric.us...n/Molded Case Circuit Breakers/0600DB0102.pdf
luckylerado
Senior Member
- Location
- Lake of the Ozarks
I am going to guess. 208/230
I would agree. If the nameplate only mentions "fuse" and fails to mention "breaker" or "over current protection (non-specific)" then to meet mfg. specs you would need to protect the equipment by a fuse. I see that about on about 5% of my inspections, normally refrigeration equipment.
- Occupation
- Licensed Electrician
I have never seen "recommended fuse size" on a piece of equipment. Make up your mind.
MCA is what size wire I use. MOCP is what I tie it to.
jojo
Member
- Location
- Philippines
- Occupation
- Electrical Engineer
In my opinion, I would go for 40AF/60AS (i.e 40Amp fused, 60Amp switch)
Based on the given:
208V, 3-ph, MCA = 25Amps
1) To check for MOCP = (1.75 to 2.25)(motor compressor full load current) per NEC440.22(A)
Find full load current first,
MCA = (1.25) (full load current)
Full load current = (25A)/1.25 = 20A
MOCP = (2)(20A) = 40A fuse; (used 2 as multiplier in this calculation)
2) For minimum disconnect switch rating = (1.15)(full load current) per NEC 440.12(A)(1) = (1.15)(20A) = 23A (minimum)
But since the MOCP in the calculation is 40A fuse, I used 60A rated switch (40AF/60AS). Let us know your thoughts.
Based on the given:
208V, 3-ph, MCA = 25Amps
1) To check for MOCP = (1.75 to 2.25)(motor compressor full load current) per NEC440.22(A)
Find full load current first,
MCA = (1.25) (full load current)
Full load current = (25A)/1.25 = 20A
MOCP = (2)(20A) = 40A fuse; (used 2 as multiplier in this calculation)
2) For minimum disconnect switch rating = (1.15)(full load current) per NEC 440.12(A)(1) = (1.15)(20A) = 23A (minimum)
But since the MOCP in the calculation is 40A fuse, I used 60A rated switch (40AF/60AS). Let us know your thoughts.
Mgraw
Senior Member
- Location
- Opelousas, Louisiana
- Occupation
- Electrician
Mitsubishi for one does it. They will give you a MCA, a Recommended fuse size(or fuse/breaker size), and a MOCP. Personally I would size it to the recommended size.
- Location
- Illinois
- Occupation
- retired electrician
If RFS is recommended fuse size, there is no issue using a 30 amp fuse.
- Occupation
- Licensed Electrician
That is so weird.
How does one decide to go above the RFS? Once someone decides to go over the RFS do they go straight to MOCP or just the next size up?
luckylerado
Senior Member
- Location
- Lake of the Ozarks
Hitachi split cools systems and Daikin as well. Must be a Japanese thing.
Mgraw
Senior Member
- Location
- Opelousas, Louisiana
- Occupation
- Electrician
As long as you are between the minimum required and the MOCP you should be good.
I have only come across "Recommended Fuse Size" on DC units. I guess it is a case of standards not keeping up with technology. Manufactures would rather fuse a unit to protect the DC converter than worry about nuisance trips.
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