# theory

1. ### Reason for usual HW shutoff valve location

In a conventional system, the standard arrangement is to have a gate valve on the (typically 28mm) cold feed pipe from cistern to cylinder. Out of curiosity, I was wondering why you won't find it on the hw pipe (typically 22mm) going out of the cylinder instead. Of course, positioned after the...
2. ### How do you calculate the complex power phase angle (φ) for reactive power calculations?

I know you can find reactive power out from the alternative formula below, but using the formula "P(W) = V(V) × I(A) × cos φ", how do you obtain the complex power phase angle (φ) from knowing the Voltage, Power and Current? Alternative formula: Reactive Power=√ (Apparent Power²– True power²)...
3. ### SL, N and L any good UK Electrical theory book?

Hi, this is my first post and I admit, I have not read the rules yet, so please go easy on me. I am not a qualified electrician but come from a science background so I know the basics quite well. Recently, I replaced an old PIR Bulk Head with a new PIR Bulk Head. While replacing the light, I...
4. ### Diversity of two single ovens?

So was doing a little paper excessive to keep by brain active. If you had: A) A single oven rated 3.5Kw (i.e. Steam oven) and B) A second single oven rated at 3.0Kw (i.e. Microwave combi oven) That would give you a current rating of 11.56A for the first oven and 10.91A for the second oven...