Tuesday, May 09, 2006

The Reason Why American Faucets Don’t Work in the United Kingdom

Here is an interesting question from Diane C. in the U.K.

I live in England and am having a LOT of trouble finding a hand shower faucet for my old clawfooted tub. I was wondering if the threading is different for the faucets you carry from the English standard threading for piping.... I have no idea if your products will be of use to me here or not. I certainly hope so as they are fabulous!!

The unfortunate answer is that U.S. faucets will not work “out of the box” with English plumbing because our standards are different. You can, however, make a few modifications to the English rough-in to fit the American faucet. Before we discuss the workaround, let’s take a look at why they don’t work in the first place.

Simply put, American plumbing threading is tapered while British plumbing threads are non-tapered. Accoring to Wikipedia, plumbing threads are tapered in the US because this allows them to self-tap slightly when torqued and form a seal as the threads compress against each other. This means that NPT fittings are easiest to make leak free with the aid of Teflon tape or a similar thread sealant compound. This standard is known as Nominal Pipe Taper (NPT) and can be seen in cross-section below:

Cross-Section of an American Threaded Plumbing Pipe (NPT Standard)

Notice that the NPT threading is on a 60 degree angle, comes to a point at each crest and is tapered.

The standard in the United Kingdom is known as BSP (British Standard Pipe Thread). Devised in 1841, this system does not taper the threads and uses a 55 degree angle between individual threads:

Cross-Section of an British Standard Pipe Thread (BSP Standard)

This is why an NPT standard American faucet will not fit a set of British supply lines that accept BSP standard faucets.

Now, you might be able to work around this by using both an American faucet and supply lines with an NPT standard rough-in threaded pipe. The NPT rough-in pipe would then have to be sweated on to the existing British interior plumbing. I have not personally tried this, but I believe it could be done relatively easily. If you live in the UK, check with your plumber first before ordering any U.S. plumbing. I would be very interested to hear how others have approached and solved this problem.