MOV breaker and conductor sizing

[ctpt]

Hi All!

I have MOVs rated at 2290VA (3ea.) and 4410VA (4ea.), all 3 phase. MOVs are fed from a 480V, 3 phase panel. The MOVs are protected by a 40A breaker (short circuit protection only) and conductor size is 3C,#12. Could you please suggest
1.if the breaker is sized correctly as per NEC.
2. does the breaker need both overload and shot circuit protection?
Please give reference to applicable NEC clauses. I have gone through Table 430.22 and 430.52, but I'm not 100% sure about MOV application.
Your suggestions would be of great help.

Thanks in advance

 

[00123456]

Kamin Dave,
Normally, over load protection is not reqd when your system connected load is below than breaker normal rated current.

For Example;
Maximum connected load = 800Ampere
Breaker Normal current = 1200Ampere

Short circuit protection is reqd for that

 

[coconutalley]

ctpt,

MOV's are for surge, voltage spikes or transient voltage protection. They are not adequate to protect overvoltages (swells) that are longer e.g. >1ms. The peak current ratings are usually for short duration spikes of 8 x 20us or 10 x 1000us. These spikes are generally cause by lightning and can be several thousand voltages. You have to pick MOVs so that it's breakover voltage is above a normal high line condition, e.g. greater than +10% of nominal peak voltage.

You need the breaker for short circuit protection. The size of the breaker depends on the wire size and your load.

 

[ctpt]

Hi 00123456,

Each MOV is protected by a 40A breaker. Considering the MOV size and conductor size, is the breaker rating OK per NEC? Normally a size 12 conductor should not have more than 20A breaker but is it true for MOV application?

 

[00123456]

Hi ctpt,

Mr.Coconutalley is saying about MOV's means it's metal oxide variaters for voltage surge protection option inbuilt in low voltage breaker, but my under standing is; you are talking about "Motorised operated Valve". Each MOV is having forward & reverse motor operation by using dual motor & dol starter. If it corrct then i will reply yo your question regarding size.

Thanks

 

[ctpt]

HI 00123456,

Yes, you are correct. I'm talking about Motor Operated Valve. I should've expnaded it earlier.
A single 480V supply goes to the actuator of the valve within which there are circuits for forward-reverse operation. I was refering to the single 480V supply breaker.
Thanks,