# Is 5V 20A power supply output safe?

I have a 5 Volt 20 Amp DC power supply. I was wondering if it is safe in terms of electricity shock due to high current output? Do I need to seal the connection to the device for protection?

Basically, I am going to connect the power supply to a string of LEDs which are all parallel (they have a series resistor to control the current of each branch). I want to know whether I need to seal the connection of the string and the power supply?

• Ever heard of ohms law? – PlasmaHH Feb 10 '17 at 14:15
• Safe for shock. Not so safe for fire, if you can short circuit the output. – Brian Drummond Feb 10 '17 at 14:20
• Well, if you use it to power a inductive load and aren't careful when you try to disconnect the load (a lectromagnet?), then there's indeed a valid risk there. – user3528438 Feb 10 '17 at 14:33
• Why the down votes? Is this not a reasonable question? – user28910 Feb 10 '17 at 14:45
• I worked with intrinsic safty devices (explosion protection) and there are power supplies with an output which is really safe, but very expensive. Which safe do you mean? – Tom Kuschel Feb 10 '17 at 14:47

That power supply can, if it's demanded of it, put out enough current to start a fire in the wires or a resistive load. The wires coming from it always need to be big enough to carry 20A safely. If they are thinner, then they need to be protected by a fuse at the power supply.

5v will not give you a shock.

If the supply is mains powered, rather than battery powered, then a fault in it could give you a shock. Commercial electronic equipment is designed so that a single fault anywhere should not give you a shock, two or more faults are required. One way is that supply is grounded. If this is the case, then you must make sure the ground wire is always connected using a 3 pin socket. If the supply only has two leads, then it is 'double insulated', and does not need earthing.

5V does not generate harmful current when touched by hands. But a short circuit is surely not a wanted thing. The sealing helps.

You did not specify, is your power supply galvanically isolated from the mains voltage. If it's not, then a proper insulative sealing is a must.

• Thanks for your answer, Basicly, I am going to connect the power supply to a string of LEDs which are all parallel (they have a serie resistor to control the current of each brunch) I want to know do I need to seal the connection of string and power supply ?! – Nima Feb 24 '17 at 15:24

Good thing you ask. If you are sure this is a 5V DC power supply then it is safe. It is always wise to measure the voltage. Please ask a adult to do so. Please take a look at Ohms law.

$$V = I \cdot R$$

You will get hurt if:

1. your body resistance (R) is too low, for instance if you are in the bathroom and your skin is wet. Or when your skin is damaged.

2. When the voltage (V) is high.

This will result in a high current stopping your heart or will burn you.

• If you are sure this is a 5V DC power supply then it is safe. So what you're basically saying here is that as long as a supply outputs 5 V, it will be safe. I'm afraid it is not that simple, the supply also needs to be isolated to be safe. There are many supplies for LEDs which are not isolated and therefore not safe to touch but they do put out a low voltage. – Bimpelrekkie Feb 10 '17 at 14:38
• Yes you are completely right thank you for the correction – Want2Know Feb 10 '17 at 14:43