It's not unusual to find mix-and-match wiring in older buildings, where most of the outlets were either installed as three-prong grounded or upgraded to three-prong grounded while a few random outlets were left as two-prong ungrounded. This is usually the result of a budget construction job that was ordered by the then-owner of the building. If you own a construction company that is trying to quickly refurbish these old houses and offices, it may be tempting to save money by leaving the electrical wiring as is, even if that means leaving those old two-prong outlets alone. But this is not something you should ignore, even if the building's owner has asked you to keep costs down as much as possible.
Indications of System Problems
Mixed grounding can be an indication that any previous work done on the electrical system was also done with a tight budget in mind. Even if the system currently tests as being OK and delivering a decent amount of power, the wiring could be just barely holding itself together. Some of the grounding might have been improperly installed as well. If you see two-prong outlets, you've got to get a utility contractor in to look at the whole system and how the ground is connected -- and to fix the ground and those two-prong outlets.
Protection and Prevention
You could have the best ground available on those three-prong outlets, but that's not going to stop someone from plugging a device into the two-prong outlet if the device's plug has only two prongs. It also won't stop someone from using a cheater plug to make a three-prong plug fit a two-prong outlet.
Here's the problem with that. The three-prong grounded outlet was created as a safety measure. Many devices have a metal case around the wiring inside them. Even if the outside is plastic or another material, you have metal inside and very close to the wires. If something happens, like faulty wire insulation lets the wire touch the metal box, there's not enough protection in the device to protect you from a shock. Even worse, if there's a massive surge of power through the electrical system in your home -- think lightning strike -- you could have power pouring out of the system and arcing toward you or anyone else in the room. With proper grounding in each outlet, all the power from the faulty wire and other sources heads down the ground wire. That's when the circuit breakers trip and cut off power to that circuit.
Even using a two-prong device in the old outlets poses a safety problem. These devices have additional built-in protection from things like faulty wires, so you'd think they'd be OK to use in those outlets. But without the ground attached to the outlet, you still risk a power surge heading into you instead of harmlessly racing along a ground wire.
Plus, really, leaving a few two-prong outlets scattered around the house or office simply looks incomplete. It looks like the cheap job it is, and people would be less likely to really want to live or work there unless there were some extremely good perks.
Make the place look great -- and make it a lot safer -- by ensuring everything is grounded properly. A utility installation contractor can help you get the system in good shape. For more information, contact companies like Bogner Construction Co .