how may RCD to use for new C U for shop (hairshop)

[mo890]

any one knows if I am correct to use only one RCD to supply two head showers and the rest ( 1 ring 2 radial 2 light 1 smoke alarm plus emerengency light ) goes on the main breaker
would appreciate the help with this
mo890

[spinlondon]

Insufficient information to provide a meaningfull answer.
Is the installation commercial?
Are the two head showers separate units, or a single unit supplying both?
Is the question in relation to a new install, or an addition or alteration to an existing installation?
I'm assuming that the installation is commercial, as such there is no requirement in BS7671 to provide RCD protection.
That however doesn't preclude additional protection by use of an RCD being provided.
Regulation 314.1 amongst other requirements, requires that an installation be divided into circuits so as to avoid hazards, and minimize inconvenience in the event of a fault.
Now if there is only one circuit which supplies just one unit, then providing RCD protection to that circuit is fine, complies with the requirements of 314.1.
However, if there are two units supplied by just one circuit, or if there are two circuits protected by a single RCD, not fine, the situation would not comply with the requirements of 314.1.
To my mind, the ideal solution would be to use two separate units, on separate circuits, with each circuit being provided with individual RCD protection.
If this is a new installation, then you could perhaps along with your client, determine that the inconveneience of having both units on a single circuit protected by a single RCD as being insignificant and outweighed by the cost of providing two separate circuits and separate RCD protection.
However, if this is an existing installation, and you are proposing adding a single RCD to protect two circuits, you would effectively be making a compliant installation into a non-compliant installation.