Is swtich mode power supply (SMPS) safely isolated?

jackrae: Slightly off-topic but if your house has either 100mA or 300mA RCD protection then it effectively offers no personal protection against electrocution. These currents are far more than required to cause fatality.

Why would anyone install a 300mA RCD ?

My shed, built by me, was wired to the then current UK 'regulations' (not actually legal requirements) which specified 30mA RCDs. That was maybe 20 years ago.

Many years ago, I was manager of a video arcade. When the power supplies failed, we replaced them with generic switch mode power supplies.

However, I found out that without grounding, just the leakage from parasitic capacitance in the power supply was enough so that the chassis would float at 1/2 of the line voltage, 60V here, and with enough current to give you a palpable shock. I discovered this by touching the chassis of two games, one with a broken ground lug on the cord, the other properly grounded.

srnet: Why would anyone install a 300mA RCD ?

My shed, built by me, was wired to the then current UK 'regulations' (not actually legal requirements) which specified 30mA RCDs. That was maybe 20 years ago.

Maybe a "repossessed" one from an industrial site/employer in the mistaken belief that they were enhancing their home safety. That said, the original poster did state the RCDs in question were 100mA and 300mA.

In the US the GFI (RCD) trips at a difference of 5 ma.

The one thing all the specifications I found essentially say bond everything to ground, with heavy wire (i.e. #12 AWG)

jackrae: Maybe a "repossessed" one from an industrial site/employer in the mistaken belief that they were enhancing their home safety. That said, the original poster did state the RCDs in question were 100mA and 300mA.

Central house RCD protection installed just after the electricity meter is rated at 300mA. Individual mains outlet circuits are protected by 30mA RCDs.

The pool supply distribution board, which then supplies pool pumps, pool light, etc, is protected by 100mA RCD.

polymorph: Many years ago, I was manager of a video arcade. When the power supplies failed, we replaced them with generic switch mode power supplies.

However, I found out that without grounding, just the leakage from parasitic capacitance in the power supply was enough so that the chassis would float at 1/2 of the line voltage, 60V here, and with enough current to give you a palpable shock. I discovered this by touching the chassis of two games, one with a broken ground lug on the cord, the other properly grounded.

Did you ground the metal enclosure of the arcade game and power supply box or the low voltage side of the power supply?

All metal enclosures shouldn't have been grounded according to local regulations anyway?

polymorph: However, I found out that without grounding, just the leakage from parasitic capacitance in the power supply was enough so that the chassis would float at 1/2 of the line voltage, 60V here, and with enough current to give you a palpable shock.

No,it wasn't "parasitic" capacitance it was the "Y" capacitors on the interference suppression module.

The 300 mA RCD is there to trip on earth faults in equipment, such as burn-out of a metal-jacketed element where the element shorts to the jacket.

The 30 mA rating is specified to protect against people actually connecting themselves from line to ground. This is a historically later consideration in the regulations.

Paul__B: No,it wasn't "parasitic" capacitance it was the "Y" capacitors on the interference suppression module.

Good point, likely correct.

Watcher: Did you ground the metal enclosure of the arcade game and power supply box or the low voltage side of the power supply?

All metal enclosures shouldn't have been grounded according to local regulations anyway?

The metal chassis inside the game is connected to the ground on the AC cord. This includes the metal doors for the coin acceptors and coin box. And probably the metal shafts on the joysticks.