Should the grind size for moka pots be as fine as that for pump espresso machines? I've seen some say mokas need fine grind size; others say fine/medium.
Should the grind size for moka pots be as fine as that for pump espresso machines?
No, pump espresso machines generally require a finer grind than moka pots.
So why does this affect grind size? In moka pots you don't want to grind too fine because the device is built for low pressure. If you grind too fine and tamp it really well then the water might not pass through as well at that low pressure. That can cause the brew to take a lot longer or it might trigger the emergency pressure valve.
With espresso machines (assuming you're using a regular filter basket, not a pressurized one) you need that finer grind so that pressure can build up. If the grind is too coarse then the water will flow through easily at lower pressure and you don't get an espresso as prescribed by some.
Of course it's possible to brew coffee using an espresso machine at lower pressure. Instead of making an espresso, that can be used to get a lungo using the same brew time.