Wiring and connector question

[redgear]

Hi everyone,

I need to connect the mains supply to my PCB board. I read that it is recommended to connect a fuse asa the power enters the product.
The power supply on the PCB converts the power to a 5v for MCU and 7-seg displays. The powered is also wired through the relay on PCB to an external load. 

The external load draws a current of 2A and inrush current peaks to a value of 21A for 185 micro seconds.  The power supply's inrush currents peak to 40A but I am not sure how long. I used online wire size calculators to calculate the size of the wire and the result was 8 AWG(i assumed the peak current of 40A. Is that correct? Should I use nominal current or inrush current ratings while selecting a wire?

What's the best way to connect these wires to the PCB, I was thinking to connect them using spade connectors. Would soldering them directly on board be a safe and reliable option?

Thanks

[Vovk_Z]

We don't use inrush current to choose a wire crossection. It depend's on rated current mostly and possible short circuit current value,  and mecanical reliability. And if we have chosen wires right they will withstand inrush currents too (they are short in time).
Mechanical reliability tells us to have wires crossection that starts from 0.5 mm2 or 0.75 mm2 - that is 24-22-20 AWG.
Then you can look for AWG table and see what current value 24-20 AWG can withstand. For example 24 AWG can withstand up to 3-4 A in chassic wiring. So it is ok for yours 2 A. I prefer to go a bit wider if there is no reasons to save money.

[redgear]

We don't use inrush current to choose a wire crossection. It depend's on rated current mostly and possible short circuit current value,  and mecanical reliability. And if we have chosen wires right they will withstand inrush currents too (they are short in time).
Mechanical reliability tells us to have wires crossection that starts from 0.5 mm2 or 0.75 mm2 - that is 24-22-20 AWG.
Then you can look for AWG table and see what current value 24-20 AWG can withstand. For example 24 AWG can withstand up to 3-4 A in chassic wiring. So it is ok for yours 2 A. I prefer to go a bit wider if there is no reasons to save money.

Thank You.

Do you suggest soldering them directly to the board or using some connectors like JST, Molex or quickonnects, etc?

[bob91343]

The inrush current will determine the wire size for long runs due to insufficient voltage at the load for small gauges.  The only reasons to use heavier wire are mechanical strength and voltage drop.  If inrush current lasts for too much time, wire heating may be a concern but how long is inrush?

[Vovk_Z]

Do you suggest soldering them directly to the board or using some connectors like JST, Molex or quickonnects, etc?

I prefer to use some suited connectors. Look what is used in professional devices. It is a large variaty. It can be any type whith enough clearance between a neutral and phase line wires.

[redgear]

The inrush current will determine the wire size for long runs due to insufficient voltage at the load for small gauges.  The only reasons to use heavier wire are mechanical strength and voltage drop.  If inrush current lasts for too much time, wire heating may be a concern but how long is inrush?

The inrush for the load is 21A for 185 microseconds. The powersupply draws a 40A inrush but I am not sure about how long it lasts.

I prefer to use some suited connectors. Look what is used in professional devices. It is a large variaty. It can be any type whith enough clearance between a neutral and phase line wires.

Ok, I will search for them

[Vovk_Z]

I still don't get what is "Load" and what is "power supply" but anyway still inrush current doesn't matter.

[Vovk_Z]

I get to my work, and now I can list some connectors which are suited and are wide used (by me or somebodyelse):
1. A3960H-03P (3 pin, 3,96 mm pitch).
2. NX5080-03 (3 pin, 5,08 mm pitch).
3. FS1536 (Faston 6.3mm x 0.8 mm) or LS1560 (Faston 4,8mm x 0.8 mm).

[redgear]

I still don't get what is "Load" and what is "power supply" but anyway still inrush current doesn't matter.

Both are loads 
The power supply is on the pcb itself powering the micro and the relay. By load I meant the external load(Lamps) which are controlled by the relay.

I get to my work, and now I can list some connectors which are suited and are wide used (by me or somebodyelse):
1. A3960H-03P (3 pin, 3,96 mm pitch).
2. NX5080-03 (3 pin, 5,08 mm pitch).
3. FS1536 (Faston 6.3mm x 0.8 mm) or LS1560 (Faston 4,8mm x 0.8 mm).

Thanks a lot for the recommendations, I will check them out.

[Vovk_Z]

1. First one is female without pins, but I think you can find male part - NS39-W3P. Contact part of it can be NS39-T.
2. Male PCB part for second is NX5080-03SMS. Cantact part if I'm not wrong is MX-08-50-0105

[redgear]

I prefer to use some suited connectors. Look what is used in professional devices. It is a large variaty. It can be any type whith enough clearance between a neutral and phase line wires.

What should be the minimum clearance between neutral and phase wires? Can I go with a 18 or 20 AWG wire for my purpose? Can the connectors be rated for the total nominal current ~3A?

[Vovk_Z]

3 A rated connectors for 2 A continuos possibly can be too loose (too weak). I wouldn't use them.
For example, good (trusty for 2 A) ones - A3960WV-03P - are of 7 A rated.
But it depends on exact type. There are more expencive 3 A rated ones with low contact resistanse (for example Molex MX-52 series, MX-5264-03) - those one possibly can do if there is a need. They are up to 0.35 mm2 (up to AWG22).

[redgear]

3 A rated connectors for 2 A continuos possibly be too loose (too weak). I wouldn'u use them.
For example, good (trusty for 2 A) ones - A3960WV-03P - are of 7 A rated.

Thanks. What about the wires, are 18 or 20 AWG's fine? What should be the minimum clearance between AC and N headers?

[Vovk_Z]

There was several topics somewhere here about creepage and distances. It could be better if you search. Sorry, I can't add something new.

[redgear]

There was several topics somewhere here about creepage and distances. It could be better if you search. Sorry, I can't add something new.

Cool, I will search for them. No problem, thanks.