It’s possible to distinguish a positive black wire from a negative black wire if you know what type of circuit the wires are in. If it’s an alternating current (AC), then black wires are positive. If it’s a direct current (DC), then black wires are negative. 

Sometimes, a circuit has two black wires. In that case, the positive black wire will be solid black while the negative black wire will have a white stripe on it. If you’re still unsure, you can use a multimeter to check.

Yes, tamper-resistant outlets are designed to be safe for use in homes with children. They feature a spring-loaded shutter that blocks the electrical slots when not in use, which helps protect children from electric shock if they try to insert an object. While they are the safest option available and highly effective, it's important to note that few things are truly 'childproof.' Children may still try to imitate adults by inserting a plug. For this reason, it's best to use tamper-resistant outlets over less effective solutions like plastic covers, which can be removed or pose a choking hazard. Always supervise young children around any electrical outlets or devices.

Licensed electricians should perform work for safety reasons; improper installations can prove hazardous or result in code violations currently.

When shopping for a multimeter to handle this job, make sure you purchase one that is able to test for capacitance. While most multimeters offer this function, some do not. You shouldn’t have to spend a lot of money to find the right multimeter. There are models that can perform this test that cost as little as $10.