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# What is the safety factor of current selection for any electrical system?

Discussion in 'The Projects Forum' started by SanRath, Nov 6, 2012.

1. ### SanRath Thread Starter New Member

Oct 28, 2010
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0
Guys,

Can you tell me the safety factor for the current we have to consider while designing an electrical system?

For example, if I have a current value of 10Amp & if I have a safety factor of 25%, then I have to design an electrical system with considering the current value of 10Amp * 25% of 10Amp = 12.5Amp.

So is there any rule or standard available for considering the safety factors?

Regards
SanRath

2. ### mcgyvr AAC Fanatic!

Oct 15, 2009
5,394
1,194
All depends on the electrical system/certifications/standards for that system.. Some may require more for "safety critical" systems. N+1 redundancy,etc..

In general though 125% of the maximum current rating is sufficient for hobbiest/consumer level products. So 12.5A for a 10A max draw.

3. ### gerty AAC Fanatic!

Aug 30, 2007
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346
You have to take a few things into consideration. Starting a motor for example may draw 200% its rated capacity under load. What is it you are designing a circuit for?

4. ### SanRath Thread Starter New Member

Oct 28, 2010
8
0
But can you tell me why it is 125%? Why not 150% or why not 200%?

Regards
SanRath

5. ### SanRath Thread Starter New Member

Oct 28, 2010
8
0

I am designing a power supply for my dispenser machine. It is related to giving an input current through 18AWG wire to 3 meanwell power supply units, Rs-50-5, RS-50-24 & SP-200-48.

As per mcgyvr reply he is telling that in general we have to consider 125% of safety factor while designing any electrical system. But why it is 125% why not 150%, why not 200%?

Regards
SanRath

6. ### GetDeviceInfo AAC Fanatic!

Jun 7, 2009
1,623
240
you should mention your location, but generally, for electrical devices, the federal electrical codes are your guide. UL or other associated agencies have thier own qualifications.

7. ### ErnieM AAC Fanatic!

Apr 24, 2011
7,991
1,848
125% is straight out of the National Electric Code (NEC). The code specs the maximum continuous current should be 80% of rated capacity, so the required rated capacity (minimum) can be found by multiplying the continuous current by 1.25.